Given an N x N matrix, mat[N][N] of integers. The task is to find the maximum value of mat(c, d) mat(a, b) over all choices of indexes such that both c > a and d > b.
Example 1:
Input:
mat[N][N] = {{ 1, 2, -1, -4, -20 },
{ -8, -3, 4, 2, 1 },
{ 3, 8, 6, 1, 3 },
{ -4, -1, 1, 7, -6 },
{ 0, -4, 10, -5, 1 }};
Output: 18
Explanation: The maximum value is 18 as mat[4][2]
- mat[1][0] = 18 has maximum difference.

Your Task:
You don't need to read input or print anything. Your task is to complete the function findMaxValue() which takes a matrix mat and returns an integer as output.
Expected Time Complexity: O(N^{2})
Expected Auxiliary Space: O(N^{2})

Constraints:
1 <= N <= 10^{3}
-10^{3}<= mat[i][j] <=10^{3}

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