Given an `m x n` matrix of integers and an integer `k`, find the max-sum submatrix such that its sum ≤ k. (Use prefix-sum plus either balanced tree or 1D max-subarray approach per row-pair.)
2D list and k.
Integer max sum.
Example 1:
Input:
matrix = [[1,0,1],[0,-2,3]] k = 2
Output:
2
Explanation:
The submatrix [[0,1],[-2,3]] has sum 2 which is max ≤ 2.