Understanding priority_queue by problem : Find K Closest Elements Solution - c++

Question

I was solving one problem on leetcode problem - Find K Closest Elements.
Here is my IDE code : ide.geeksforgeeks
#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
std::vector<int> findClosestElements(std::vector<int>& arr, int k, int x)
{
std::vector<int> res;
// min heap
std::priority_queue<std::pair<int, int>, std::vector<std::pair<int, int>>,
std::greater<std::pair<int, int>>> pq;
std::cout << "Debug queue : \n";
for (auto it : arr)
{
int closest = abs(it - x);
pq.push(std::make_pair(closest, it));
//std::cout << closest << " : " << it << "\n";
if (pq.size() > k)
{
pq.pop();
}
}
std::cout << "\nIterating queue : \n";
while(!pq.empty())
{
res.push_back(pq.top().second);
std::cout << pq.top().first << " : " << pq.top().second << "\n";
pq.pop();
}
std::sort(res.begin(), res.end());
return res;
}
int main()
{
std::vector<int> arr = {1,2,3,4,5};
auto res = findClosestElements(arr, 4, 3);
return 0;
}
While I was iterating the queue, I can not see the minimum number : 0 : 3 which should be the top element of priority_queue. Can anyone please suggest?

Answer 1

Max heaps solves the problem.
vector<int> findClosestElements(vector<int>& arr, int k, int x)
{
std::vector<int> res;
std::priority_queue<std::pair<int, int>> pq;
for (auto it : arr)
{
int closest = abs(it - x);
//std::cout << closest << " : " << it << "\n";
pq.push(std::make_pair(closest, it));
if (pq.size() > k)
{
pq.pop();
}
}
//std::cout << "\nDebug queue : \n";
while(!pq.empty())
{
res.push_back(pq.top().second);
//std::cout << pq.top().first << " : " << pq.top().second << "\n";
pq.pop();
}
std::sort(res.begin(), res.end());
return res;
}