[LeetCode September Challange]Day24-Find the Difference

Given two strings s and t which consist of only lowercase letters.

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

Find the letter that was added in t.

Example:

Input:
s = "abcd"
t = "abcde"

Output:
e

Explanation:
'e' is the letter that was added.

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Solution

Time complexity : O(n)
Space complexity : O(1)

class Solution {
public:
    char findTheDifference(string s, string t) {
        char res = 0;
        
        for (char c: t) res ^= c;
        for (char c: s) res ^= c;
        
        return res;
    }
};

總共會出現的字：2A + b，其中A為s、t共同出現，b為只出現在t。

全部xor，A會被消掉，剩下b，即ans。