Permutations in Go

permutations.go

func permutations(a []int) [][]int {
	var results [][]int
	permute(a, 0, func(a []int) {
		results = append(results, a)
	})
	return results
}

func permute(a []int, start int, f func([]int)) {
	if start >= len(a) {
		c := make([]int, len(a))
		copy(c, a)
		f(c)
		return
	}

	for i := start; i < len(a); i++ {
		a[i], a[start] = a[start], a[i]
		permute(a, start+1, f)
		a[start], a[i] = a[i], a[start]
	}
}