Let A be an N by M matrix in which every row and every column is sorted.
Given i1, j1, i2, and j2, compute the number of elements of M smaller than M{i1, j1} and larger than M{i2, j2}.
For example, given the following matrix:
{{1, 3, 7, 10, 15, 20}, {2, 6, 9, 14, 22, 25}, {3, 8, 10, 15, 25, 30}, {10, 11, 12, 23, 30, 35}, {20, 25, 30, 35, 40, 45}}
And i1 = 1, j1 = 1, i2 = 3, j2 = 3, return 15 as there are 15 numbers in the matrix smaller than 6 or greater than 23.