LeetCode 347. Top K Frequent Elements

Given a non-empty array of integers, return the k most frequent elements.

For example,
Given [1,1,1,2,2,3] and k = 2, return [1,2].

hashmap + heap

#include <vector>#include <iostream>#include <queue>#include <unordered_map>using namespace std;// Using a hashmaptypedef pair<int, int> data;vector<int> topKFrequent(vector<int>& nums, int k) {  vector<int> res;  unordered_map<int, int> numToCount;  for(int i = 0; i < nums.size(); ++i) {    if(numToCount.find(nums[i]) == numToCount.end()) {      numToCount.insert({nums[i], 1});    } else {      ++numToCount[nums[i]];    }  }  priority_queue<data, vector<data>, greater<data> > minHeap;  auto iter = numToCount.begin();  while(iter != numToCount.end()) {    minHeap.push(make_pair(iter->second, iter->first));    if(minHeap.size() > k) {minHeap.pop();}    iter++;  }  while(!minHeap.empty()) {    res.push_back(minHeap.top().second);    minHeap.pop();  }  return res;}int main(void) {  vector<int> nums{1, 1, 1, 2, 2, 3};  vector<int> res = topKFrequent(nums, 2);  for(int i = 0; i < res.size(); ++i) cout << res[i] << endl;}