C++ Python用XOR sum解字串問題Leetcode 389 find the difference

C++ Python用XOR sum解字串問題Leetcode 389 find the difference。字串 t 是透過隨機打亂字串 s 產生的，然後在隨機位置再添加一個字母。找出那個添加的字母

[codes on Leetcode]https://leetcode.com/problems/find-the-difference/solutions/4086491/c-python-frequencies-vs-xor-vs-sum-0ms-beats-100-math-explains/