Leet Code Daily 2024-07-23 - Sort Array by Increasing Frequency

class Solution {
public:
    vector<int> frequencySort(vector<int>& nums) {
        unordered_map<int, int> freq;
        for (const auto& num : nums) {
            freq[num]++;
        }
        map<int, vector<int>> freq_to_nums;
        for (const auto& pair : freq) {
            freq_to_nums[pair.second].push_back(pair.first);
        }
        vector<int> ret;
        for (auto& pair : freq_to_nums) {
            sort(pair.second.begin(), pair.second.end(), std::greater<>());
            for (const auto& num : pair.second) {
                for (int i = 0; i < pair.first; i++) {
                    ret.push_back(num);
                }
            }
        }
        return ret;
    }
};