Challenge problem 3

This is simply the two-dimensional version of problem 2. You are given an n-by-n matrix of numbers. What is the submatrix with the largest sum?

For example, for the input

10	5	-3	-2	-6
0	5	-3	-2	6
-6	-6	3	-2	16
-4	5	3	-2	8
0	5	-3	-2	6

Then answer is highlighted in green.

There is a O(n³) algorithm, where n is as in "n-by-n matrix".