389. 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:eExplanation:'e' is the letter that was added.

class Solution {public:    char findTheDifference(string s, string t) {        string tmp=s.length()>t.length()?s:t;        string mi=s.length()<t.length()?s:t;        unordered_map<int,int> a;        for (int i=0;i<tmp.length();i++)             a[tmp[i]]++;        for (int i=0;i<mi.length();i++)             a[mi[i]]--;        for (unordered_map<int,int>::iterator it=a.begin();it!=a.end();++it)            if (it->second)                return (char)(it->first);        return NULL;    }};