Check if two string slices are equal by checking if they are a permutation of the other

permutations_test.go

package main

import (
	"testing"
	"github.com/stretchr/testify/require"
)

func TestIsPerm(t *testing.T) {
	ts := []struct {
		xs, ys []string
		ok     bool
		rs     []int
	}{
		{
			xs: []string{"a", "b"},
			ys: []string{},
			ok: false,
		},
		{
			xs: []string{"a"},
			ys: []string{"b"},
			ok: false,
		},
		{
			xs: []string{"a", "b"},
			ys: []string{"b", "a"},
			rs: []int{1, 0},
			ok: true,
		},
	}
	for _, j := range ts {
		ok, rs := isPerm(j.xs, j.ys)
		require.Equal(t, j.ok, ok)
		if ok {
			require.Equal(t, j.rs, rs)
		}
	}
}

func isPerm(xs, ys []string) (ok bool, rs []int) {
	ok = len(xs) == len(ys)
	rs = make([]int, 0, len(xs))
	for ok && len(xs) != 0 {
		var i int
		ok, i = exists(ys, xs[0])
		if ok {
			rs = append(rs, i)
			xs, ys = removeAt(xs, 0), removeAt(ys, i)
		}
	}
	return
}

func exists(xs []string, x string) (ok bool, i int) {
	for !ok && i < len(xs) {
		ok = xs[i] == x
		if !ok {
			i++
		}
	}
	return
}

func removeAt(xs []string, i int) (rs []string) {
	if len(xs) == i-1 {
		rs = xs[:i]
	} else {

		rs = append(xs[:i], xs[i+1:]...)
	}
	return
}