Sort Characters By Frequency 题解

题目如下：

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

Example:

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.

统计字母频率并且最后组合起来即可，代码如下：

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;


bool com(vector<char> a, vector<char> b) {
return a.size() > b.size();
}


string frequencySort(string s) {
vector<vector<char> > count;
//char t = s[0];
vector<char> k;
k.push_back(s[0]);
count.push_back(k);
int flag = 0;
for (int i = 1; i < s.size(); i++) {
flag = 0;
for (int l = 0; l < count.size(); l++) {
if (s[i] == count[l][0]) {
count[l].push_back(s[i]);
flag = 1;
break;
}
}
if (flag == 0) {
vector<char> p;
p.push_back(s[i]);
count.push_back(p);
}
}
sort(count.begin(), count.end(), com);
string result;
for (int i = 0; i < count.size(); i++) {
for (int l = 0; l < count[i].size(); l++) {
result += count[i][l];
}
}
return result;
}