Given a matrix and an integer k, return the maximum sum of any rectangle (a contiguous sub-matrix) whose sum is no larger than k. It is guaranteed at least one such rectangle exists. The input is JSON {matrix, k}.
Input: JSON {matrix, k}.
Output: Integer — the maximum rectangle sum <= k.
Input: {"matrix":[[1,0,1],[0,-2,3]],"k":2}
Output: 2
Explanation: A rectangle sums to exactly 2.Input: {"matrix":[[2,2,-1]],"k":3}
Output: 3
Explanation: Best sum not exceeding 3.1<=rows,cols<=100-10^5<=value<=10^5