面试题 01.02：判定是否互为字符重排

输入: s1 = "abc", s2 = "bca"
输出: true 

输入: s1 = "abc", s2 = "bad"
输出: false

class Solution {
public:
    bool CheckPermutation(string s1, string s2) {
        unordered_map<char,int> map;
        for(char c:s1){
            map[c]++;
        }
        for(char c:s2){
            if(map[c]==0) return false;//s2有额外的字符
            else map[c]--;
        }
        for(char c:s1){
            if(map[c]>0) return false;//s1有额外的字符
        }
        return true;
    }
};