Go function that returns the permutations of a slice.

permute.go

func permute[T any](v []T) [][]T {
	switch len(v) {
	case 0:
		return [][]T{
			{},
		}
	case 1:
		return [][]T{
			{v[0]},
		}
	}
	result := make([][]T, 0, factorial(len(v)))
	for i := range v {
		for _, p := range permute(pop(v, i, i+1)) {
			result = append(result, append([]T{v[i]}, p...))
		}
	}
	return result
}

func factorial(n int) int {
	result := 1
	for i := 1; i <= n; i++ {
		result *= i
	}
	return result
}

// pop returns a new slice that doesn't contain the elements s[i:j].
func pop[T any](s []T, i, j int) []T {
	ss := make([]T, 0, len(s)-1)
	ss = append(ss, s[:i]...)
	ss = append(ss, s[j:]...)
	return ss
}