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permutation

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permutation

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permutation
===========

A permutation library for Golang.

Use **NewPerm()** to generate a **Pemutator**, the argument *k* must be a **non-nil slice**,and the argument *less* must be a Less function that **implements compare functionality of k's element type**. If k's element is ordered,argument *less* can be nil.For ordered in Golang, visit http://golang.org/ref/spec#Comparison_operators
 ```Go
	func NewPerm(k interface{}, less Less) (*Permutator, error) 
```
  After generating a Permutator, the argument k can be modified and deleted,Permutator store a copy of k internel.A Permutator can  be used concurrently
  
  Invoke **Permutator.Next()** to return the next permutation in lexcial order.If all permutations generated,return an error
```Go
	func (p *Permutator) Next()(interface{}, error)
```	
  Invoke **Permutator.NextN()** to return the next n permuation in lexical order.
```Go
  func (p *Permutator) NextN() interface{}
```
  The returned interface{} can be modified,it does nothing to do with the Permutator

Invoke **Permutator.Left()** to return the number of ungenerated permutation
```Go
	func (p Permutator) Left() int
```
Invoke **Permutator.Index()** to return the index of last permutation, which start from 1 to n! (n is the length of slice)
```Go
	func (p Permutator) Index() int
```
  Invoke **Permutator.Reset()** to reset the permutator
```Go
  func (p *Permutator) Reset()
```
  Invoke **Permutator.MoveIndex()** to move the current index position of the permutator
```Go
  func (p *Permutator) MoveIndex(index int) (int, error)
```
If successful, the integer value of the new index position is returned. If an error occurs, an error is return and the index position will not be adjusted.

An example:
```Go
	func main() {
		i := []int{1,2,3}
		p,err:=NewPerm(i,nil) //generate a Permutator
		if err != nil {
			fmt.Println(err)
			return
		}
		for i,err:=p.Next();err==nil;i,err=p.Next(){
			fmt.Printf("%3d permutation: %v left %d\n",p.Index()-1,i.([]int),p.Left())
		}
	}
```
--------------------------------------
outputs:

1 permutation: [1 2 3] left 5
	  2 permutation: [1 3 2] left 4
	  3 permutation: [2 1 3] left 3
	  4 permutation: [2 3 1] left 2
	  5 permutation: [3 1 2] left 1
	  6 permutation: [3 2 1] left 0

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permutation

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