leetcode 389. Find the Difference

问题描述

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.

解题代码

利用 hashtable 计数，大于 0 表示在 s 中出现，小于 0 表示该字符在 t 中出现的次数多于在 s 中出现的次数。

class Solution {
public:
	char findTheDifference(const string &s, const string &t) {
		map<char, int> m;

		for (size_t i = 0; i < s.length(); i++) {
			m[s[i]]++;
		}

		for (size_t i = 0; i < t.length(); i++) {
			if (--m[t[i]] < 0) {
				return t[i];
			}
		}

		return 0;
	}
};