leetcode

#include <array>
using namespace std;
static constexpr array<pair<int,int>, 256> init_array() {
        array<pair<int,int>,256> alphabet;
        for (int i = 0; i != 256; ++i) {
            alphabet[i].first = 0;
            alphabet[i].second = i;
        }
        return alphabet;
    }
class Solution {
private:
    static inline constexpr array<pair<int,int>,256> init = init_array();
public:
    string frequencySort(string s) {
        array<pair<int,int>,256> alphabet = init;
        for (unsigned char c : s) {
            ++alphabet[c].first;
        }
        sort(alphabet.begin(), alphabet.end(), std::greater{});
        string res;
        res.reserve(s.size());
        for (int i = 0; i != 256 && alphabet[i].first != 0; ++i) {
            for (int j = 0; j != alphabet[i].first; ++j) {
                res.push_back(alphabet[i].second);
            }
        }
        return res;
    }
};