Largest rectangular sub matrix with the number difference k

问题

Input: A 2-dimensional array NxN - Matrix - with numbers from 0 to 9.

Output: Largest rectangular area where absolute value of number's difference in area is k.

Possible input:

int k=3;
const int N=5;
int matrix[N][N] = {{9, 3, 8, 2, 0},
                    {2, 7, 6, 8, 5},
                    {8, 5, 7, 7, 6},
                    {3, 0, 4, 0, 9},
                    {7, 2, 0, 4, 0}};

Is it related to find largest area in histogram problem? If it does how I can transform this matrix two binary matrix? And how to approach this kind of problems?

Answer: largest area is 8 by following sub matrix {{7, 6, 8, 6}, {5, 7, 7, 6}}

What I think should be done:

1. Transform matrix to binary matrix
2. Create histogram from binary matrix
3. Calculate largest area using largest area in histogram.

What is unclear is how to transform input matrix to binary matrix.

来源：https://stackoverflow.com/questions/25965492/largest-rectangular-sub-matrix-with-the-number-difference-k