golang permutations; ref:http://www.geocities.jp/m_hiroi/golang/yagp02.html

necklace_permutations.go

package main

import "fmt"

func main() {
	p := []string{"Tokyo", "Kyoto", "Osaka", "Nagoya"}
	res := createPermurations(p)
	fmt.Printf("%v\n", res)
}


func createPermurations(cities []string) [][]string {
	max := len(cities)
	var result [][]int
	for i := 1; i < max; i++ {
		list := []int{i, 0}
		permutations(&result, list, 1, max)
	}

	perms := make([][]string, len(result))
	for i, list := range result {
		perm := make([]string, len(cities))
		for j, idx := range list {
			perm[j] = cities[idx]
		}
		perms[i] = perm
	}
	return perms
}

func permutations(result *[][]int, list []int, n, max int) []int {
	if len(list) == max {
		return list
	}
	for i := 1; i < max; i++ {
		switch {
		case i == 1 && list[0] <= i:
			continue
		case isMember(list, i):
			continue
		}
		l := permutations(result, append(list, i), n+1, max)
		if l != nil {
			*result = append(*result,l)
		}
	}
	return nil
}

func isMember(list []int, city int) bool {
	for _, v := range list {
		if v == city {
			return true
		}
	}
	return false
}

permiutations.go

package main

import "fmt"

func main() {
	p := []string{"Tokyo", "Kyoto", "Osaka", "Nagoya"}
	res := createPermurations(p)
	fmt.Printf("%v\n", res)
}

func createPermurations(cities []string) [][]string {
	var result [][]string
	var list []string
	return permutations(result, cities, list)
}

func permutations(result [][]string, cities, list []string) [][]string {
	if len(list) == len(cities) {
		return append(result, list)
	}
	for _, city := range cities {
		if isMember(list, city) {
			continue
		}
		result = permutations(result, cities, append(list, city))
	}
	return result
}

func isMember(list []string, city string) bool {
	for _, v := range list {
		if v == city {
			return true
		}
	}
	return false
}