1504 - Count Submatrices With All Ones.

Medium

Given an m x n binary matrix mat, return the number of submatrices that have all ones.

Example 1:

Input: mat = \[\[1,0,1],1,1,0,1,1,0]

Output: 13

Explanation:

There are 6 rectangles of side 1x1.

There are 2 rectangles of side 1x2.

There are 3 rectangles of side 2x1.

There is 1 rectangle of side 2x2.

There is 1 rectangle of side 3x1.

Total number of rectangles = 6 + 2 + 3 + 1 + 1 = 13.

Example 2:

Input: mat = \[\[0,1,1,0],0,1,1,1,1,1,1,0]

Output: 24

Explanation:

There are 8 rectangles of side 1x1.

There are 5 rectangles of side 1x2.

There are 2 rectangles of side 1x3.

There are 4 rectangles of side 2x1.

There are 2 rectangles of side 2x2.

There are 2 rectangles of side 3x1.

There is 1 rectangle of side 3x2.

Total number of rectangles = 8 + 5 + 2 + 4 + 2 + 2 + 1 = 24.

Constraints:

• 1 <= m, n <= 150

• mat[i][j] is either 0 or 1.