LC 347 K most Frequent - C++ bucket sort - source code blog: http://xpharry.org/2016/06/23/347-top-k-frequent-elements-my-submissions-questioneditorial-solution/

LC347KMostFrequentBucketSort1.cpp

class Solution {
public:
    vector<int> topKFrequent(vector<int>& nums, int k) {
        unordered_map<int,int> m;
        for(int num : nums) {
            m[num]++;
        }
        
        vector<vector<int>> buckets(nums.size()+1);
        for(auto p : m) {
            buckets[p.second].push_back(p.first); // second:frequency, first:num
        }
        
        vector<int> ans;
        for(int i = buckets.size()-1; i >= 0 && ans.size() < k; --i) {
            for(int num : buckets[i]) {
                ans.push_back(num);
                if(ans.size() == k)
                    break; // this can only jump out the inner loop
            }
        }
        
        return ans;
    }
};