LeetCode 451. Sort Characters By Frequency

解题思路:使用map 将string里面的每个字符insert进去,之后需要对map的value进行一个降序,考虑到无法直接对map的值进行降序排列,所以把map 放到vector容器中,这样可以对vector直接排序,最后字符串转string,return 即可.

class Solution {public:        string frequencySort(string s) {        //排序        if(s.length() == 0)        return "";        map<char,int>s_map;        for(int i = 0; i < s.length(); i++){            s_map[s[i]]++;        }        vector< pair<char,int> >s_res(s_map.begin(),s_map.end());        sort(s_res.begin(),s_res.end(),CmpByValue());        char s_c[s.length()];        int k = 0;        for(int i = 0; i < s_res.size(); i++){            for(int j = 0; j < s_res[i].second; j++){                //int k = s_res[i].second;                s_c[j+k] = s_res[i].first;                cout<<s_res[i].first<<" "<<endl;            }            k += s_res[i].second;        }        string res(s_c,s.length());        return res;    }private:    struct CmpByValue {  bool operator()(const pair<char,int>& p1, const pair<char,int>& p2) {    return p1.second > p2.second;  }};};