recover_pass.go

package main

import (
	"bytes"
	"crypto/md5"
	"fmt"
	"testing"
)

// There is a database with hashed user passwords (hashPassword function).
// There is also a known set of characters that can be used in passwords (variable alphabet).
// It is necessary to implement the RecoverPassword function so that it recovers the password using a known hash and TestRecoverPassword succeeds

var alphabet = "abcd123"

func recoverPass(h []byte, i int, s string) string {
	if i == 0 {
		if bytes.Equal(h, hashPassword(s)) {
			return s
		}
		return ""
	}
	for _, c := range alphabet {
		if s := recoverPass(h, i-1, s+string(c)); len(s) > 0 {
			return s
		}
	}
	return ""
}

func RecoverPassword(h []byte) string {
	for i := 1; i <= 7; i++ {
		s := recoverPass(h, i, "")
		if len(s) > 0 {
			return s
		}
	}
	return ""
}

func TestRecoverPassword(t *testing.T) {
	for _, exp := range []string{
		"a",
		"12",
		"abc333d",
	} {
		t.Run(exp, func(t *testing.T) {
			act := RecoverPassword(hashPassword(exp))
			if act != exp {
				t.Errorf("recovered: %q expected: %q", act, exp)
			}
		})
	}
}

func hashPassword(in string) []byte {
	h := md5.Sum([]byte(in))
	return h[:]
}