C#: Kth smallest Element in row-wise and column-wise sorted 2D array

Difficulty Level: MEDIUM

Problem Statement:

Given an n x n matrix, where every row and column is sorted in non-decreasing order. Find the kth smallest element in the given 2D array.

Input:

k = 3 and array =

        10, 20, 30, 40

        15, 25, 35, 45

        24, 29, 37, 48

        32, 33, 39, 50

Output:

The 7th smallest element is 30