Practice-Coding-Questions

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Practice-Coding-Questions

★ 44 Open GitHub ↗

Practice set for SWE interview prep. Includes my personal solutions for Leetcode, CTCI, SPOJ, etc.

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# Practice-Coding-Questions

Personal Practice Set - Doing One a Day (sometimes) in a Variety of Languages (Mostly Python)!

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---

## Leetcode

|  # | Difficulty | Problem                                                                                      | Solution                                                          |
| -- | ---------- | -------------------------------------------------------------------------------------------- | ----------------------------------------------------------------- |
| 1  | Easy       | [Two Sum](leetcode/1-Easy-Two-Sum/problem.md)                                                | [Java](leetcode/1-Easy-Two-Sum/answer.java), [Python](leetcode/1-Easy-Two-Sum/answer.py), [Ruby](leetcode/1-Easy-Two-Sum/answer.rb)|
| 2  | Medium     | [Add Two Numbers](leetcode/2-Medium-Add-Two-Numbers/problem.md)                              | [C](leetcode/2-Medium-Add-Two-Numbers/answer.c)                   |
| 3  | Medium     | [Longest Substring Without Repeating Characters](leetcode/3-Medium-Longest-Substring-Without-Repeating-Characters/problem.md) | [Python](leetcode/3-Medium-Longest-Substring-Without-Repeating-Characters/answer.py) |
| 4  | Hard       | [Median of Two Sorted Arrays](leetcode/4-Hard-Median-Of-Two-Sorted-Arrays/problem.md)        | [Python](leetcode/4-Hard-Median-Of-Two-Sorted-Arrays/answer.py)   |
| 5  | Medium     | [Longest Palindromic Substring](leetcode/5-Medium-Longest-Palindromic-Substring/problem.md)  | [Python](leetcode/5-Medium-Longest-Palindromic-Substring/answer.py) |
| 6  | Medium     | [Zig Zag Conversion](leetcode/6-Medium-Zig-Zag-Conversion/problem.md)                        | [Java](leetcode/6-Medium-Zig-Zag-Conversion/answer.java)          |
| 7  | Easy       | [Reverse Integer](leetcode/7-Easy-Reverse-Integer/problem.md)                                | [Python](leetcode/7-Easy-Reverse-Integer/answer.py)               |
| 8  | Medium     | [String to Integer](leetcode/8-Medium-Atoi/problem.md)                                       | [Ruby](leetcode/8-Medium-Atoi/answer.rb)                          |
| 9  | Easy       | [Palindrome Number](leetcode/9-Easy-Palindrome-Number/problem.md)                            | [C](leetcode/9-Easy-Palindrome-Number/answer.c), [Java](leetcode/9-Easy-Palindrome-Number/answer.java), [Python](leetcode/9-Easy-Palindrome-Number/answer.py), [Swift](leetcode/9-Easy-Palindrome-Number/answer.swift) |
| 10 | Hard       | [Regular Expression Matching](leetcode/10-Hard-Regular-Expression-Matching/problem.md)       | [Python](leetcode/10-Hard-Regular-Expression-Matching/answer.py)  |
| 11 | Medium     | [Container With Most Water](leetcode/11-Medium-Container-With-Most-Water/problem.md)         | [Python](leetcode/11-Medium-Container-With-Most-Water/answer.py)  |
| 12 | Medium     | [Integer to Roman](leetcode/12-Medium-Integer-To-Roman/problem.md)                           | [Python](leetcode/12-Medium-Integer-To-Roman/answer.py)           |
| 13 | Easy       | [Roman to Integer](leetcode/13-Easy-Roman-To-Integer/problem.md)                             | [C](leetcode/13-Easy-Roman-To-Integer/answer.c), [Python](leetcode/13-Easy-Roman-To-Integer/answer.py)|
| 14 | Easy       | [Longest Common Prefix](leetcode/14-Easy-Longest-Common-Prefix/problem.md)                   | [Python](leetcode/14-Easy-Longest-Common-Prefix/answer.py)        |
| 15 | Medium     | [3Sum](leetcode/15-Medium-3Sum/problem.md)                                                   | [Python](leetcode/15-Medium-3Sum/answer.py)                       |
| 16 | Medium     | [3Sum Closest](leetcode/16-Medium-3Sum-Closest/problem.md)                                   | [Python](leetcode/16-Medium-3Sum-Closest/answer.py)               |
| 17 | Medium     | [Letter Combinations of a Phone Number](leetcode/17-Medium-Letter-Combinations-Of-A-Phone-Number/problem.md) | [Python](leetcode/17-Medium-Letter-Combinations-Of-A-Phone-Number/answer.py) |
| 18 | Medium     | [4Sum](leetcode/18-Medium-4Sum/problem.md)                                                   | [Python](leetcode/18-Medium-4Sum/answer.py)                       |
| 19 | Medium     | [Remove Nth Node From End of List](leetcode/19-Medium-Remove-Nth-Node-From-End-Of-List/problem.md) | [Python](leetcode/19-Medium-Remove-Nth-Node-From-End-Of-List/answer.py) |
| 20 | Easy       | [Valid Parentheses](leetcode/20-Easy-Valid-Parentheses/problem.md)                           | [Java](leetcode/20-Easy-Valid-Parentheses/answer.java), [Python](leetcode/20-Easy-Valid-Parentheses/answer.py) |
| 21 | Easy       | [Merge Two Sorted Lists](leetcode/21-Easy-Merge-Two-Sorted-Lists/problem.md)                 | [Java](leetcode/21-Easy-Merge-Two-Sorted-Lists/answer.java), [Python](leetcode/21-Easy-Merge-Two-Sorted-Lists/answer.py)|
| 22 | Medium     | [Generate Parentheses](leetcode/22-Medium-Generate-Parentheses/problem.md)                   | [Python](leetcode/22-Medium-Generate-Parentheses/answer.py)       |
| 23 | Hard       | [Merge k Sorted Lists](leetcode/23-Hard-Merge-K-Sorted-Lists/problem.md)                     | [Python](leetcode/23-Hard-Merge-K-Sorted-Lists/answer.py)         |
| 24 | Medium     | [Swap Node in Pairs](leetcode/24-Medium-Swap-Nodes-In-Pairs/problem.md)                      | [Python](leetcode/24-Medium-Swap-Nodes-In-Pairs/answer.py)        |
| 25 | Hard       | [Reverse Nodes in k-Group](leetcode/25-Hard-Reverse-Nodes-In-K-Group/problem.md)             | [Python](leetcode/25-Hard-Reverse-Nodes-In-K-Group/answer.py)     |
| 26 | Easy       | [Remove Duplicates from Sorted Array](leetcode/26-Easy-Remove-Duplicates-From-Sorted-Array/problem.md) | [C](leetcode/26-Easy-Remove-Duplicates-From-Sorted-Array/answer.c), [Python](leetcode/26-Easy-Remove-Duplicates-From-Sorted-Array/answer.py) |
| 27 | Easy       | [Remove Element](leetcode/27-Easy-Remove-Element/problem.md)                                 | [Python](leetcode/27-Easy-Remove-Element/answer.py)               |
| 28 | Easy       | [Implement strStr()](leetcode/28-Easy-Implement-strStr/problem.md)                           | [C](leetcode/28-Easy-Implement-strStr/answer.c), [Python](leetcode/28-Easy-Implement-strStr/answer.py) |
| 29 | Medium     | [Divide Two Integers](leetcode/29-Medium-Divide-Two-Integers/problem.md)                     | [Python](leetcode/29-Medium-Divide-Two-Integers/answer.py)        |
| 31 | Medium     | [Next Permutation](leetcode/31-Medium-Next-Permutation/problem.md)                           | [Python](leetcode/31-Medium-Next-Permutation/answer.py)           |
| 33 | Medium     | [Search in Rotated Sorted Array](leetcode/33-Medium-Search-In-Rotated-Sorted-Array/problem.md) | [Python](leetcode/33-Medium-Search-In-Rotated-Sorted-Array/answer.py) |
| 34 | Medium     | [Find First and Last Position of Element in Sorted Array](leetcode/34-Medium-Find-First-And-Last-Position-Of-Element-In-Sorted-Array/problem.md) | [Python](leetcode/34-Medium-Find-First-And-Last-Position-Of-Element-In-Sorted-Array/answer.py) |
| 35 | Easy       | [Search Insert Position](leetcode/35-Easy-Search-Insert-Position/problem.md)                 | [Go](leetcode/35-Easy-Search-Insert-Position/answer.go), [Java](leetcode/35-Easy-Search-Insert-Position/answer.java), [JavaScript](leetcode/35-Easy-Search-Insert-Position/answer.js), [Scala](leetcode/35-Easy-Search-Insert-Position/answer.scala) |
| 36 | Medium     | [Valid Sudoku](leetcode/36-Medium-Valid-Sudoku/problem.md)                                   | [Python](leetcode/36-Medium-Valid-Sudoku/answer.py)               |
| 38 | Easy       | [Count and Say](leetcode/38-Easy-Count-And-Say/problem.md)                                   | [Python](leetcode/38-Easy-Count-And-Say/answer.py)                |
| 39 | Medium     | [Combination Sum](leetcode/39-Medium-Combination-Sum/problem.md)                             | [Python](leetcode/39-Medium-Combination-Sum/answer.py)            |
| 40 | Medium     | [Combination Sum II](leetcode/40-Medium-Combination-Sum-II/problem.md)                       | [Python](leetcode/40-Medium-Combination-Sum-II/answer.py)         |
| 42 | Hard       | [Trapping Rain Water](leetcode/42-Hard-Trapping-Rain-Water/problem.md)                       | [Python](leetcode/42-Hard-Trapping-Rain-Water/answer.py)          |
| 43 | Medium     | [Multiply Strings](leetcode/43-Medium-Multiply-Strings/problem.md)                           | [Python](leetcode/43-Medium-Multiply-Strings/answer.py)           |
| 44 | Hard       | [Wildcard Matching](leetcode/44-Hard-Wildcard-Matching/problem.md)                           | [Python](leetcode/44-Hard-Wildcard-Matching/answer.py)            |
| 46 | Medium     | [Permutations](leetcode/46-Medium-Permutations/problem.md)                                   | [Python](leetcode/46-Medium-Permutations/answer.py)               |
| 47 | Medium     | [Permutations II](leetcode/47-Medium-Permutations-II/problem.md)                             | [Python](leetcode/47-Medium-Permutations-II/answer.py)            |
| 48 | Medium     | [Rotate Image](leetcode/48-Medium-Rotate-Image/problem.md)                                   | [Python](leetcode/48-Medium-Rotate-Image/answer.py)               |
| 49 | Medium     | [Group Anagrams](leetcode/49-Medium-Group-Anagrams/problem.md)                               | [Python](leetcode/49-Medium-Group-Anagrams/answer.py)             |
| 50 | Medium     | [Pow(x, n)](leetcode/50-Medium-Pow(x,n)/problem.md)                                          | [Python](leetcode/50-Medium-Pow(x,n)/answer.py)                   |
| 53 | Easy       | [Maximum Subarray](leetcode/53-Easy-Maximum-Subarray/problem.md)                             | [Java](leetcode/53-Easy-Maximum-Subarray/answer.java)             |
| 54 | Medium     | [Spiral Matrix](leetcode/54-Medium-Spiral-Matrix/problem.md)                                 | [Python](leetcode/54-Medium-Spiral-Matrix/answer.py)              |
| 55 | Medium     | [Jump Game](leetcode/55-Medium-Jump-Game/problem.md)                                         | [Python](leetcode/55-Medium-Jump-Game/answer.py)                  |
| 56 | Medium     | [Merge Intervals](leetcode/56-Medium-Merge-Intervals/problem.md)                             | [Python](leetcode/56-Medium-Merge-Intervals/answer.py)            |
| 58 | Easy       | [Length of Last Word](leetcode/58-Easy-Length-Of-Last-Word/problem.md)                       | [Python](leetcode/58-Easy-Length-Of-Last-Word/answer.py)          |
| 62 | Medium     | [Unique Paths](leetcode/62-Medium-Unique-Paths/problem.md)                                   | [Python](leetcode/62-Medium-Unique-Paths/answer.py)               |
| 63 | Medium     | [Unique Paths II](leetcode/63-Medium-Unique-Paths-II/problem.md)                             | [Python](leetcode/63-Medium-Unique-Paths-II/answer.py)            |
| 64 | Medium     | [Minimum Path Sum](leetcode/64-Medium-Minimum-Path-Sum/problem.md)                           | [Python](leetcode/64-Medium-Minimum-Path-Sum/answer.py)           |
| 66 | Easy       | [Plus One](leetcode/66-Easy-Plus-One/problem.md)                                             | [Python](leetcode/66-Easy-Plus-One/answer.py)                     |
| 67 | Easy       | [Add Binary](leetcode/67-Easy-Add-Binary/problem.md)                                         | [Python](leetcode/67-Easy-Add-Binary/answer.py)                   |
| 69 | Easy       | [Sqrt()](leetcode/69-Easy-Sqrt/problem.md)                                                   | [Python](leetcode/69-Easy-Sqrt/answer.py)                         |
| 70 | Easy       | [Climbing Stairs](leetcode/70-Easy-Climbing-Stairs/problem.md)                               | [C](leetcode/70-Easy-Climbing-Stairs/answer.c)                    |
| 76 | Hard       | [Minimum Window Substring](leetcode/76-Hard-Minimum-Window-Substring/problem.md)             | [Python](leetcode/76-Hard-Minimum-Window-Substring/answer.py)     |
| 78 | Medium     | [Subsets](leetcode/78-Medium-Subsets/problem.md)                                             | [Python](leetcode/78-Medium-Subsets/answer.py)                    |
| 79 | Medium     | [Word Search](leetcode/79-Medium-Word-Search/problem.md)                                     | [Python](leetcode/79-Medium-Word-Search/answer.py)                |
| 83 | Easy       | [Remove Duplicates from Sorted List](leetcode/83-Easy-Remove-Duplicates-From-Sorted-List/problem.md) | [Python](leetcode/83-Easy-Remove-Duplicates-From-Sorted-List/answer.py)|
| 84 | Hard       | [Largest Rectangle in Histogram](leetcode/84-Hard-Largest-Rectangle-In-Histogram/problem.md) | [Python](leetcode/84-Hard-Largest-Rectangle-In-Histogram/answer.py)|
| 85 | Hard       | [Maximal Rectangle](leetcode/85-Hard-Maximal-Rectangle/problem.md)                           | [Python](leetcode/85-Hard-Maximal-Rectangle/answer.py)            |
| 88 | Easy       | [Merge Sorted Array](leetcode/88-Easy-Merge-Sorted-Array/problem.md)                         | [Python](leetcode/88-Easy-Merge-Sorted-Array/answer.py)           |
| 100| Easy       | [Same Tree](leetcode/100-Easy-Same-Tree/problem.md)                                          | [Python](leetcode/100-Easy-Same-Tree/answer.py)                   |
| 101| Easy       | [Symmetric Tree](leetcode/101-Easy-Symmetric-Tree/problem.md)                                | [Python](leetcode/101-Easy-Symmetric-Tree/answer.py)              |
| 102| Medium     | [Binary Tree Level Order Traversal](leetcode/102-Medium-Binary-Tree-Level-Order-Traversal/problem.md) | [Python](leetcode/102-Medium-Binary-Tree-Level-Order-Traversal/answer.py)|
| 104| Easy       | [Maximum Depth of Binary Tree](leetcode/104-Easy-Maximum-Depth-Of-Binary-Tree/problem.md)    | [Python](leetcode/104-Easy-Maximum-Depth-Of-Binary-Tree/answer.py)|
| 105| Medium     | [Construct Binary Tree from Preorder and Inorder Traversal](leetcode/105-Medium-Construct-Binary-Tree-From-Preorder-And-Inorder-Traversal/problem.md) | [Python](leetcode/105-Medium-Construct-Binary-Tree-From-Preorder-And-Inorder-Traversal/answer.py)|
| 106| Medium     | [Construct Binary Tree from Inorder and Postorder Traversal](leetcode/106-Medium-Construct-Binary-Tree-From-Inorder-And-Postorder-Traversal/problem.md) | [Python](leetcode/106-Medium-Construct-Binary-Tree-From-Inorder-And-Postorder-Traversal/answer.py)|
| 107| Easy       | [Binary Tree Level Order Traversal II](leetcode/107-Easy-Binary-Tree-Level-Order-Traversal-II/problem.md) | [Python](leetcode/107-Easy-Binary-Tree-Level-Order-Traversal-II/answer.py)|
| 108| Easy       | [Convert Sorted Array to Binary Search Tree](leetcode/108-Convert-Sorted-Array-To-Binary-Search-Tree/problem.md) | [Python](leetcode/108-Convert-Sorted-Array-To-Binary-Search-Tree/answer.py)|
| 110| Easy       | [Balanced Binary Tree](leetcode/110-Easy-Balanced-Binary-Tree/problem.md)                    | [Python](leetcode/110-Easy-Balanced-Binary-Tree/answer.py)        |
| 111| Easy       | [Minimum Depth of Binary Tree](leetcode/111-Easy-Minimum-Depth-Of-Binary-Tree/problem.md)    | [Python](leetcode/111-Easy-Minimum-Depth-Of-Binary-Tree/answer.py)|
| 112| Easy       | [Path Sum](leetcode/112-Easy-Path-Sum/problem.md)                                            | [Python](leetcode/112-Easy-Path-Sum/answer.py)                    |
| 118| Easy       | [Pascal's Triangle](leetcode/118-Easy-Pascal's-Triangle/problem.md)                          | [Python](leetcode/118-Easy-Pascal's-Triangle/answer.py)           |
| 121| Easy       | [Best Time to Buy and Sell Stock](leetcode/121-Easy-Best-Time-To-Buy-And-Sell-Stock/problem.md) | [Python](leetcode/121-Easy-Best-Time-To-Buy-And-Sell-Stock/answer.py) |
| 122| Easy       | [Best Time to Buy and Sell Stock II](leetcode/122-Easy-Best-Time-To-Buy-And-Sell-Stock-II/problem.md) | [Python](leetcode/122-Easy-Best-Time-To-Buy-And-Sell-Stock-II/answer.py) |
| 123| Hard       | [Best Time to Buy and Sell Stock III](leetcode/123-Hard-Best-Time-To-Buy-And-Sell-Stock-III/problem.md) | [Python](leetcode/123-Hard-Best-Time-To-Buy-And-Sell-Stock-III/answer.py) |
| 125| Easy       | [Valid Palindrome](leetcode/125-Easy-Valid-Palindrome/problem.md)                            | [Python](leetcode/125-Easy-Valid-Palindrome/answer.py)            |
| 127| Medium     | [Word Ladder](leetcode/127-Medium-Word-Ladder/problem.md)                                    | [Python](leetcode/127-Medium-Word-Ladder/answer.py)               |
| 133| Medium     | [Clone Graph](leetcode/133-Medium-Clone-Graph/problem.md)                                    | [Python](leetcode/133-Medium-Clone-Graph/answer.py)               |
| 136| Easy       | [Single Number](leetcode/136-Easy-Single-Number/problem.md)                                  | [Python](leetcode/136-Easy-Single-Number/answer.py)               |
| 137| Medium     | [Single Number II](leetcode/137-Medium-Single-Number-II/problem.md)                          | [Python](leetcode/137-Medium-Single-Number-II/answer.py)          |
| 139| Medium     | [Word Break](leetcode/139-Medium-Word-Break/problem.md)                                      | [Python](leetcode/139-Medium-Word-Break/answer.py)                |
| 141| Easy       | [Linked List Cycle](leetcode/141-Easy-Linked-List-Cycle/problem.md)                          | [Python](leetcode/141-Easy-Linked-List-Cycle/answer.py)           |
| 142| Medium     | [Linked List Cycle II](leetcode/142-Medium-Linked-List-Cycle-II/problem.md)                  | [Python](leetcode/142-Medium-Linked-List-Cycle-II/answer.py)      |
| 146| Hard       | [LRU Cache](leetcode/146-Hard-LRU-Cache/problem.md)                                          | [Python](leetcode/146-Hard-LRU-Cache/answer.py)                   |
| 148| Medium     | [Sort List](leetcode/148-Medium-Sort-List/problem.md)                                        | [Python](leetcode/148-Medium-Sort-List/answer.py)                 |
| 153| Medium     | [Find Minimum in Rotated Sorted Array](leetcode/153-Medium-Find-Minimum-In-Rotated-Sorted-Array/problem.md) | [Python](leetcode/153-Medium-Find-Minimum-In-Rotated-Sorted-Array/answer.py)|
| 155| Easy       | [Min Stack](leetcode/155-Easy-Min-Stack/problem.md)                                          | [Python](leetcode/155-Easy-Min-Stack/answer.py)                   |
| 162| Medium     | [Find Peak Element](leetcode/162-Medium-Find-Peak-Element/problem.md)                        | [Python](leetcode/162-Medium-Find-Peak-Element/answer.py)         |
| 168| Easy       | [Excel Sheet Column Title](leetcode/168-Easy-Excel-Sheet-Column-Title/problem.md)            | [Python](leetcode/168-Easy-Excel-Sheet-Column-Title/answer.py)    |
| 171| Easy       | [Excel Sheet Column Number](leetcode/171-Easy-Excel-Sheet-Column-Number/problem.md)          | [Python](leetcode/171-Easy-Excel-Sheet-Column-Number/answer.py)   |
| 173| Medium     | [Binary Search Tree Iterator](leetcode/173-Medium-Binary-Search-Tree-Iterator/problem.md)    | [Python](leetcode/173-Medium-Binary-Search-Tree-Iterator/answer.py) |
| 188| Hard       | [Best Time to Buy and Sell Stock IV](leetcode/188-Hard-Best-Time-To-Buy-And-Sell-Stock-IV/problem.md) | [Python](leetcode/188-Hard-Best-Time-To-Buy-And-Sell-Stock-IV/answer.py) |
| 191| Easy       | [Number of 1 Bits](leetcode/191-Easy-Number-Of-1-Bits/problem.md)                            | [Python](leetcode/191-Easy-Number-Of-1-Bits/answer.py)            |
| 196| Easy       | [Delete Duplicate Emails](leetcode/196-Easy-Delete-Duplicate-Emails/problem.md)              | [SQL](leetcode/196-Easy-Delete-Duplicate-Emails/answer.sql)       |
| 200| Medium     | [Number of Islands](leetcode/200-Medium-Number-Of-Islands/problem.md)                        | [Python](leetcode/200-Medium-Number-Of-Islands/answer.py)         |
| 204| Easy       | [Count Primes](leetcode/204-Easy-Count-Primes/problem.md)                                    | [Python](leetcode/204-Easy-Count-Primes/answer.py)                |
| 206| Easy       | [Reverse Linked List](leetcode/206-Easy-Reverse-Linked-List/problem.md)                      | [Python](leetcode/206-Easy-Reverse-Linked-List/answer.py)         |
| 207| Medium     | [Course Schedule](leetcode/207-Medium-Course-Schedule/problem.md)                            | [Python](leetcode/207-Medium-Course-Schedule/answer.py)           |
| 208| Medium     | [Implement Trie](leetcode/208-Medium-Implement-Trie/problem.md)                              | [Java](leetcode/208-Medium-Implement-Trie/answer.java), [Python](leetcode/208-Medium-Implement-Trie/answer.py)|
| 215| Medium     | [Kth Largest Element in an Array](leetcode/215-Medium-Kth-Largest-Element-In-An-Array/problem.md) | [Python](leetcode/215-Medium-Kth-Largest-Element-In-An-Array/answer.py)|
| 218| Hard       | [The Skyline Problem](leetcode/218-Hard-The-Skyline-Problem/problem.md)                      | [Python](leetcode/218-Hard-The-Skyline-Problem/answer.py)         |
| 226| Easy       | [Invert Binary Tree](leetcode/226-Easy-Invert-Binary-Tree/problem.md)                        | [Python](leetcode/226-Easy-Invert-Binary-Tree/answer.py)          |
| 231| Easy       | [Power Of Two](leetcode/231-Easy-Power-Of-Two/problem.md)                                    | [Python](leetcode/231-Easy-Power-Of-Two/answer.py)                |
| 234| Easy       | [Palindrome Linked List](leetcode/234-Easy-Palindrome-Linked-List/problem.md)                | [Python](leetcode/234-Easy-Palindrome-Linked-List/answer.py)      |
| 235| Easy       | [Lowest Common Ancestor of a Binary Search Tree](leetcode/235-Easy-Lowest-Common-Ancestor-Of-A-Binary-Search-Tree/problem.md) | [Python](leetcode/235-Easy-Lowest-Common-Ancestor-Of-A-Binary-Search-Tree/answer.py)|
| 236| Medium     | [Lowest Common Ancestor of a Binary Tree](leetcode/236-Medium-Lowest-Common-Ancestor-Of-A-Binary-Tree/problem.md) | [Python](leetcode/236-Medium-Lowest-Common-Ancestor-Of-A-Binary-Tree/answer.py)|
| 237| Easy       | [Delete Node in a Linked List](leetcode/237-Easy-Delete-Node-In-A-Linked-List/problem.md)    | [Python](leetcode/237-Easy-Delete-Node-In-A-Linked-List/answer.py)|
| 238| Medium     | [Product of Array Except Self](leetcode/238-Medium-Product-Of-Array-Except-Self/problem.md)  | [Python](leetcode/238-Medium-Product-Of-Array-Except-Self/answer.py)|
| 240| Medium     | [Search a 2D Matrix II](leetcode/240-Medium-Search-A-2D-Matrix-II/problem.md)                | [Python](leetcode/240-Medium-Search-A-2D-Matrix-II/answer.py)     |
| 258| Easy       | [Add Digits](leetcode/235-Easy-Add-Digits/problem.md)                                        | [Python](leetcode/235-Easy-Add-Digits/answer.py)                  |
| 268| Easy       | [Missing Number](leetcode/268-Easy-Missing-Number/problem.md)                                | [Python](leetcode/268-Easy-Missing-Number/answer.py)              |
| 273| Hard       | [Integer to English Words](leetcode/273-Hard-Integer-To-English-Words/problem.md)            | [Python](leetcode/273-Hard-Integer-To-English-Words/answer.py)    |
| 283| Easy       | [Move Zeroes](leetcode/283-Easy-Move-Zeroes/problem.md)                                      | [Python](leetcode/283-Easy-Move-Zeroes/answer.py)                 |
| 287| Medium     | [Find the Duplicate Number](leetcode/287-Medium-Find-The-Duplicate-Number/problem.md)        | [Python](leetcode/287-Medium-Find-The-Duplicate-Number/answer.py) |
| 295| Hard       | [Find Median from Data Stream](leetcode/295-Hard-Find-Median-From-Data-Stream/problem.md)    | [Python](leetcode/295-Hard-Find-Median-From-Data-Stream/answer.py)|
| 297| Hard       | [Serialize and Deserialize Binary Tree](leetcode/297-Hard-Serialize-And-Deserialize-Binary-Tree/problem.md) | [Java](leetcode/297-Hard-Serialize-And-Deserialize-Binary-Tree/answer.java) |
| 301| Hard       | [Remove Invalid Parentheses](leetcode/301-Hard-Remove-Invalid-Parentheses/problem.md)        | [Python](leetcode/301-Hard-Remove-Invalid-Parentheses/answer.py)  |
| 310| Medium     | [Minimum Height Trees](leetcode/310-Medium-Minimum-Height-Trees/problem.md)                  | [Python](leetcode/310-Medium-Minimum-Height-Trees/answer.py)      |
| 341| Medium     | [Flatten Nested List Iterator](leetcode/341-Medium-Flatten-Nested-List-Iterator/problem.md)  | [Python](leetcode/341-Medium-Flatten-Nested-List-Iterator/answer.py) |
| 344| Easy       | [Reverse String](leetcode/344-Easy-Reverse-String/problem.md)                                | [Python](leetcode/344-Easy-Reverse-String/answer.py)              |
| 388| Medium     | [Longest Absolute File Path](leetcode/388-Medium-Longest-Absolute-File-Path/problem.md)      | [Python](leetcode/388-Medium-Longest-Absolute-File-Path/answer.py)|
| 389| Easy       | [Find the Difference](leetcode/389-Easy-Find-The-Difference/problem.md)                      | [Python](leetcode/389-Easy-Find-The-Difference/answer.py)         |
| 461| Easy       | [Hamming Distance](leetcode/461-Easy-Hamming-Distance/problem.md)                            | [Python](leetcode/461-Easy-Hamming-Distance/answer.py)            |
| 495| Medium     | [Teemo Attacking](leetcode/495-Medium-Teemo-Attacking/problem.md)                            | [Python](leetcode/495-Medium-Teemo-Attacking/answer.py)           |
| 535| Medium     | [Encode and Decode TinyURL](leetcode/535-Medium-Encode-And-Decode-TinyURL/problem.md)        | [Python](leetcode/535-Medium-Encode-And-Decode-TinyURL/answer.py) |
| 733| Easy       | [Flood Fill](leetcode/733-Easy-Flood-Fill/problem.md)                                        | [Python](leetcode/733-Easy-Flood-Fill/answer.py)                  |
| 771| Easy       | [Jewels and Stones](leetcode/771-Easy-Jewels-And-Stones/problem.md)                          | [Python](leetcode/771-Easy-Jewels-And-Stones/answer.py)           |
|1114| Easy       | [Print in Order](leetcode/1114-Easy-Print-In-Order/problem.md)                               | [Python](leetcode/1114-Easy-Print-In-Order/answer.py)             |

---

## SPOJ

|  # | Difficulty | Problem                                                                                      | Solution                                                        |
| -- | ---------- | -------------------------------------------------------------------------------------------- | --------------------------------------------------------------- |
| 1  | Easy       | [Life, the Universe, and Everything](SPOJ/1-Life-Universe-Everything/problem.md)             | [C](SPOJ/1-Life-Universe-Everything/answer.c)                   |
| 2  |            |                                                                                              |                                                                 |
| 3  |            |                                                                                              |                                                                 |

---

## Hackerrank

30 Days of Code Challenge

| Day| Difficulty | Problem                                                                                      | Solution                                                        |
| -- | ---------- | -------------------------------------------------------------------------------------------- | --------------------------------------------------------------- |
| 0  | Easy       | [Hello, World.](https://www.hackerrank.com/challenges/30-hello-world)                        | [Java](hackerrank/30-days-of-code/day-0.java)                   |
| 1  | Easy       | [Data Types](https://www.hackerrank.com/challenges/30-data-types)                            | [Java](hackerrank/30-days-of-code/day-1.java)                   |
| 2  | Easy       | [Operators](https://www.hackerrank.com/challenges/30-operators)                              | [Java](hackerrank/30-days-of-code/day-2.java)                   |
| 3  | Easy       | [Conditional Statements](https://www.hackerrank.com/challenges/30-conditional-statements)    | [Python](hackerrank/30-days-of-code/day-3.py)                   |
| 4  | Easy       | [Class vs Instance](https://www.hackerrank.com/challenges/30-class-vs-instance)    	         | [Python](hackerrank/30-days-of-code/day-4.py)                   |
| 5  | Easy       | [Loops](https://www.hackerrank.com/challenges/30-loops)                                      | [Python](hackerrank/30-days-of-code/day-5.py)                   |
| 6  | Easy       | [Let's Review](https://www.hackerrank.com/challenges/30-review-loop)    	     	         | [Python](hackerrank/30-days-of-code/day-6.py)                   |
| 7  | Easy       | [Arrays](https://www.hackerrank.com/challenges/30-arrays)	    	   	     	             | [Python](hackerrank/30-days-of-code/day-7.py)                   |
| 8  | Easy       | [Dictionaries and Maps](https://www.hackerrank.com/challenges/30-dictionaries-and-maps)      | [Python](hackerrank/30-days-of-code/day-8.py)                   |
| 9  | Easy       | [Recursion](https://www.hackerrank.com/challenges/30-recursion)   				             | [Python](hackerrank/30-days-of-code/day-9.py)                   |
| 10 | Easy       | [Binary Number](https://www.hackerrank.com/challenges/30-binary-numbers)	        		 | [Python](hackerrank/30-days-of-code/day-10.py)                  |
| 11 | Easy       | [2D Arrays](https://www.hackerrank.com/challenges/30-2d-arrays)			                     | [Python](hackerrank/30-days-of-code/day-11.py)                  |
| 12 | Easy       | [Inheritance](https://www.hackerrank.com/challenges/30-inheritance)		  		             | [Python](hackerrank/30-days-of-code/day-12.py)                  |
| 13 | Easy       | [Abstract Classes](https://www.hackerrank.com/challenges/30-abstract-classes)  		         | [Python](hackerrank/30-days-of-code/day-13.py)                  |
| 14 | Easy       | [Scope](https://www.hackerrank.com/challenges/30-scope)	 				                     | [Python](hackerrank/30-days-of-code/day-14.py)                  |
| 15 | Easy       | [Linked List](https://www.hackerrank.com/challenges/30-linked-list)				             | [Python](hackerrank/30-days-of-code/day-15.py)                  |
| 16 | Easy       | [Exceptions - String to Integer](https://www.hackerrank.com/challenges/30-exceptions-string-to-integer) | [Python](hackerrank/30-days-of-code/day-16.py)       |
| 17 | Easy       | [More Exceptions](https://www.hackerrank.com/challenges/30-more-exceptions)                  | [Python](hackerrank/30-days-of-code/day-17.py)                  |
| 18 | Easy       | [Queues and Stacks](https://www.hackerrank.com/challenges/30-queues-stacks)    	             | [Python](hackerrank/30-days-of-code/day-18.py)                  |
| 19 | Easy       | [Interfaces](https://www.hackerrank.com/challenges/30-interfaces) 	                         | [Java](hackerrank/30-days-of-code/day-19.java)                  |
| 20 | Easy       | [Sorting](https://www.hackerrank.com/challenges/30-sorting)    	                             | [Python](hackerrank/30-days-of-code/day-20.py)                  |
| 21 | Easy       | [Generics](https://www.hackerrank.com/challenges/30-generics)	                             | [Java](hackerrank/30-days-of-code/day-21.java)                  |
| 22 | Easy       | [Binary Search Trees](https://www.hackerrank.com/challenges/30-binary-search-trees/)         | [Java](hackerrank/30-days-of-code/day-22.java)                  |
| 23 | Easy       | [BST Level-Order Traversal](https://www.hackerrank.com/challenges/30-binary-trees/)          | [Python](hackerrank/30-days-of-code/day-23.py)                  |
| 24 | Easy       | [More Linked Lists](https://www.hackerrank.com/challenges/30-linked-list-deletion/)          | [Python](hackerrank/30-days-of-code/day-24.py)                  |
| 25 | Medium     | [Running Time and Complexity](https://www.hackerrank.com/challenges/30-running-time-and-complexity/) | [Python](hackerrank/30-days-of-code/day-25.py)          |
| 26 | Easy       | [Nested Logic](https://www.hackerrank.com/challenges/30-nested-logic/)                       | [Python](hackerrank/30-days-of-code/day-26.py)                  |
| 27 | Easy       | [Testing](https://www.hackerrank.com/challenges/30-testing/)                                 | [Python](hackerrank/30-days-of-code/day-27.py)                  |
| 28 | Medium     | [RegEx, Patterns, and Intro to Databases](https://www.hackerrank.com/challenges/30-regex-patterns/) | [Python](hackerrank/30-days-of-code/day-28.py)           |
| 29 | Medium     | [Bitwise AND](https://www.hackerrank.com/challenges/30-bitwise-and/)                         | [Python](hackerrank/30-days-of-code/day-29.py)                  |

---

## CTCI

Cracking the Coding Interview 6th Edition Python Solutions

|  # | Difficulty | Problem                                                                                      | Solution                                                        |
| -- | ---------- | -------------------------------------------------------------------------------------------- | --------------------------------------------------------------- |
| 1.1|            | Is Unique                                                                                    | [Python](CTCI/Chapter1/1.1-Is_Unique.py)                        |
| 1.2|            | Check Permutation                                                                            | [Python](CTCI/Chapter1/1.2-Check_Permutation.py)                |
| 1.3|            | URLify                                                                                       | [Python](CTCI/Chapter1/1.3-URLify.py)                           |
| 1.4|            | Palindrome Permutation                                                                       | [Python](CTCI/Chapter1/1.4-Palindrome_Permutation.py)           |
| 1.5|            | One Away                                                                                     | [Python](CTCI/Chapter1/1.5-One_Away.py)                         |
| 1.6|            | String Compression                                                                           | [Python](CTCI/Chapter1/1.6-String_Compression.py)               |
| 1.7|            | Rotate Matrix                                                                                | [Python](CTCI/Chapter1/1.7-Rotate_Matrix.py)                    |
| 1.8|            | Zero Matrix                                                                                  | [Python](CTCI/Chapter1/1.8-Zero_Matrix.py)                      |
| 1.9|            | String Rotation                                                                              | [Python](CTCI/Chapter1/1.9-String_Rotation.py)                  |
|    |            |                                                                                              |                                                                 |
| 2.1|            | Remove Dups                                                                                  | [Python](CTCI/Chapter2/2.1-Remove_Dups.py)                      |
| 2.2|            | Return Kth to Last                                                                           | [Python](CTCI/Chapter2/2.2-Return_Kth_To_Last.py)               |
| 2.3|            | Delete Middle Node                                                                           | [Python](CTCI/Chapter2/2.3-Delete_Middle_Node.py)               |
| 2.4|            | Partition                                                                                    | [Python](CTCI/Chapter2/2.4-Partition.py)                        |
| 2.5|            | Sum Lists                                                                                    | [Python](CTCI/Chapter2/2.5-Sum_Lists.py)                        |
| 2.6|            | Palindrome                                                                                   | [Python](CTCI/Chapter2/2.6-Palindrome.py)                       |
| 2.7|            | Intersection                                                                                 | [Python](CTCI/Chapter2/2.7-Intersection.py)                     |
| 2.8|            | Loop Detection                                                                               | [Python](CTCI/Chapter2/2.8-Loop_Detection.py)                   |
|    |            |                                                                                              |                                                                 |
| 3.1|            | Three in One                                                                                 | [Python](CTCI/Chapter3/3.1-Three_In_One.py)                     |
| 3.2|            | Stack Min                                                                                    | [Python](CTCI/Chapter3/3.2-Stack_Min.py)                        |
| 3.3|            | Stack of Plates                                                                              | [Python](CTCI/Chapter3/3.3-Stack_Of_Plates.py)                  |
|    |            |                                                                                              |                                                                 |
| 4.1|            | Route Between Nodes                                                                          | [Python](CTCI/Chapter4/4.1-Route_Between_Nodes.py)              |
| 4.2|            | Minimal Tree                                                                                 | [Python](CTCI/Chapter4/4.2-Minimal_Tree.py)                     |
| 4.3|            | List of Depths                                                                               | [Python](CTCI/Chapter4/4.3-List_Of_Depths.py)                   |
| 4.4|            | Check Balanced                                                                               | [Python](CTCI/Chapter4/4.4-Check_Balanced.py)                   |
| 4.5|            | Validate BST                                                                                 | [Python](CTCI/Chapter4/4.5-Validate_BST.py)                     |
| 4.6|            | Successor                                                                                    | [Python](CTCI/Chapter4/4.6-Successor.py)                        |
| 4.7|            | Build Order                                                                                  | [Python](CTCI/Chapter4/4.7-Build_Order.py)                      |
| 4.8|            | First Common Ancestor                                                                        | [Python](CTCI/Chapter4/4.8-First_Common_Ancestor.py)            |
| 4.9|            | BST Sequences                                                                                | [Python](CTCI/Chapter4/4.9-BST_Sequences.py)                    |
|4.10|            | Check Subtree                                                                                | [Python](CTCI/Chapter4/4.10-Check_Subtree.py)                   |
|4.11|            | Random Node                                                                                  | [Python](CTCI/Chapter4/4.11-Random_Node.py)                     |
|4.12|            | Paths With Sum                                                                               | [Python](CTCI/Chapter4/4.12-Paths_With_Sum.py)                  |
|    |            |                                                                                              |                                                                 |
| 5.1|            | Insertion                                                                                    | [Coming Soon](CTCI/Chapter5/5.1-Insertion.py)                   |
|    |            |                                                                                              |                                                                 |
| 8.1|            | Triple Step                                                                                  | [Python](CTCI/Chapter8/8.1-Triple_Step.py)                      |
| 8.2|            | Robot in a Grid                                                                              | [Python](CTCI/Chapter8/8.2-Robot_in_a_Grid.py)                  |
| 8.3|            | Magic Index                                                                                  | [Python](CTCI/Chapter8/8.3-Magic_Index.py)                      |
| 8.4|            | Power Set                                                                                    | [Python](CTCI/Chapter8/8.4-Power_Set.py)                        |
| 8.5|            | Recursive Multiply                                                                           | [Python](CTCI/Chapter8/8.5-Recursive_Multiply.py)               |
| 8.6|            | Towers of Hanoi                                                                              |                                                                 |
| 8.7|            | Permutations Without Dups                                                                    | [Python](CTCI/Chapter8/8.7-Permutations_Without_Dups.py)        |
| 8.8|            | Permutations With Dups                                                                       | [Python](CTCI/Chapter8/8.8-Permutations_With_Dups.py)           |
|    |            |                                                                                              |                                                                 |
|17.1|            | Add Without Plus                                                                             | [Python](CTCI/Chapter17/17.1-Add_Without_Plus.py)               |

---

## Google Foobar Challenge

|  # | Level	  | Problem                                                                                      | Solution                                                        |
| -- | ---------- | -------------------------------------------------------------------------------------------- | --------------------------------------------------------------- |
| 1  | 1          | [Solar Doomsday](Google_Foobar/Solar_Doomsday/problem.md)                                    | [Java](Google_Foobar/Solar_Doomsday/answer.java)                |
| 2  | 2          | [Gearing Up For Destruction](Google_Foobar/Gearing_Up_For_Destruction/problem.md)            | [Python](Google_Foobar/Gearing_Up_For_Destruction/answer.py)    |
| 3  | 2          | [Lovely Lucky Lambs](Google_Foobar/Lovely_Lucky_Lambs/problem.md)                            | [Python](Google_Foobar/Lovely_Lucky_Lambs/answer.py)            |

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