---
title: 'LeetCode 389. Find the Difference'
disqus: hackmd
---

# LeetCode 389. Find the Difference

## Description

You are given two strings s and t.

String t is generated by random shuffling string s and then add one more letter at a random position.

Return the letter that was added to t.

## Example

Input: s = "abcd", t = "abcde"
Output: "e"
Explanation: 'e' is the letter that was added.

Input: s = "", t = "y"
Output: "y"

## Constraints

0 <= s.length <= 1000
t.length == s.length + 1
s and t consist of lowercase English letters.

## Answer

此題一樣使用XOR做兩次會不見的概念來先將 s全部做XOR，然後對t做XOR即可得多出來的值。

// 2021_11_07
char findTheDifference(char * s, char * t) {
    if(*s == '\0'){return *t;}
    if(*t == '\0'){return *s;}
    char ans = *s++;
    while(*s != '\0' || *t != '\0'){
        if(*s != '\0'){ans ^= *s++;}
        if(*t != '\0'){ans ^= *t++;}
    }
    return ans;
}

## Link
https://leetcode.com/problems/find-the-difference/
###### tags: `Leetcode`