leetcode 451. Sort Characters By Frequency

Given a string, sort it in decreasing order based on the frequency of characters.

Example 1:

Input:
“tree”

Output:
“eert”

Explanation:
‘e’ appears twice while ‘r’ and ‘t’ both appear once.
So ‘e’ must appear before both ‘r’ and ‘t’. Therefore “eetr” is also a valid answer.
Example 2:

Input:
“cccaaa”

Output:
“cccaaa”

Explanation:
Both ‘c’ and ‘a’ appear three times, so “aaaccc” is also a valid answer.
Note that “cacaca” is incorrect, as the same characters must be together.
Example 3:

Input:
“Aabb”

Output:
“bbAa”

Explanation:
“bbaA” is also a valid answer, but “Aabb” is incorrect.
Note that ‘A’ and ‘a’ are treated as two different characters.

题意很简单，就是一个简单的排序，

代码如下：

#include <iostream>#include <vector>#include <map>#include <set>#include <queue>#include <stack>#include <string>#include <climits>#include <algorithm>#include <sstream>#include <functional>#include <bitset>using namespace std;bool cmp(pair<char, int> a , pair<char, int> b){    return a.second > b.second;}class Solution {public:    string frequencySort(string s)     {        map<char, int> mmp;        for (char a : s)        {            if (mmp.find(a) == mmp.end())                mmp[a] = 1;            else                mmp[a] += 1;        }        vector<pair<char, int>> res(mmp.begin(),mmp.end());        sort(res.begin(), res.end(), cmp);        string tmp = "";        for (pair<char, int> a : res)        {            for (int i = 0; i < a.second; i++)                tmp += a.first;        }        return tmp;    }};