378. Kth Smallest Element in a Sorted Matrix - LeetCode Solution

class Solution:
    def kthSmallest(self, matrix: List[List[int]], k: int) -> int:
        import heapq
        arr = []
        
        for i in range(len(matrix)):
            for j in range(len(matrix[i])):
                arr.append(matrix[i][j])
                
        heapq.heapify(arr)
        
        arr = list(heapq.nsmallest(k, arr))
        
        return arr[-1]