Lexicographical permutation

permutation.go

package main

import (
    "fmt"
    "time"
)

func nextPermutation(slice []int) bool {
    var k int
    for k = len(slice) - 2; k >= 0; k-- {
        if slice[k] < slice[k+1] {
            break
        }
    }

    if k == -1 {
        return false
    }

    var l int
    for l = len(slice) - 1; l >= 0; l-- {
        if slice[k] < slice[l] {
            break
        }
    }

    slice[k], slice[l] = slice[l], slice[k]

    for i, j := k+1, len(slice)-1; i < j; i, j = i+1, j-1 {
        slice[i], slice[j] = slice[j], slice[i]
    }

    return true
}

func main() {
    d := []int{1, 0, 2, 3, 4, 5, 6, 7, 8, 9}
    fmt.Println(d)
    t0 := time.Now()
    for nextPermutation(d) {
    }
    fmt.Println(d)
    t1 := time.Now()

    fmt.Printf("Time taken: %v\n", t1.Sub(t0))
}