Kth element in Matrix.cpp

/*
Kth element in Matrix
=====================

Given a N x N matrix, where every row and column is sorted in non-decreasing order. Find the kth smallest element in the matrix.

Example 1:
Input:
N = 4
mat[][] =     {{16, 28, 60, 64},
                   {22, 41, 63, 91},
                   {27, 50, 87, 93},
                   {36, 78, 87, 94 }}
K = 3
Output: 27
Explanation: 27 is the 3rd smallest element.

Example 2:
Input:
N = 4
mat[][] =     {{10, 20, 30, 40}
                   {15, 25, 35, 45}
                   {24, 29, 37, 48}
                   {32, 33, 39, 50}}
K = 7
Output: 30
Explanation: 30 is the 7th smallest element.

Your Task:
You don't need to read input or print anything. Complete the function kthsmallest() which takes the mat, N and K as input parameters and returns the kth smallest element in the matrix.

Expected Time Complexity: O(N*Log(N))
Expected Auxiliary Space: O(N)

Constraints:
1 <= N <= 50
1 <= mat[][] <= 10000
1 <= K <= N*N
*/

int kthSmallest(int mat[MAX][MAX], int n, int k)
{
  priority_queue<pair<int, pair<int, int>>, vector<pair<int, pair<int, int>>>, greater<pair<int, pair<int, int>>>> pq;
  for (int i = 0; i < n; i++)
    pq.push({mat[0][i], {0, i}});
  for (int i = 0; i < k - 1; i++)
  {
    auto x = pq.top();
    pq.pop();
    if (x.second.first < n - 1)
    {
      pq.push({mat[x.second.first + 1][x.second.second], {x.second.first + 1, x.second.second}});
    }
  }
  return pq.top().first;
}