# GeetCode Hub

Given a `rows * columns` matrix `mat` of ones and zeros, return how many submatrices 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.
```

Example 3:

```Input: mat = [[1,1,1,1,1,1]]
Output: 21
```

Example 4:

```Input: mat = [[1,0,1],[0,1,0],[1,0,1]]
Output: 5
```

Constraints:

• `1 <= rows <= 150`
• `1 <= columns <= 150`
• `0 <= mat[i][j] <= 1`

class Solution { public int numSubmat(int[][] mat) { } }