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# Count Square Submatrices with All Ones

Given a `m * n` matrix of ones and zeros, return how many **square** submatrices have all ones.

**Example 1:**

```
Input: matrix =
[
  [0,1,1,1],
  [1,1,1,1],
  [0,1,1,1]
]
Output: 15
Explanation: 
There are 10 squares of side 1.
There are 4 squares of side 2.
There is  1 square of side 3.
Total number of squares = 10 + 4 + 1 = 15.
```

**Example 2:**

```
Input: matrix = 
[
  [1,0,1],
  [1,1,0],
  [1,1,0]
]
Output: 7
Explanation: 
There are 6 squares of side 1.  
There is 1 square of side 2. 
Total number of squares = 6 + 1 = 7.
```

**Constraints:**

* `1 <= arr.length <= 300`
* `1 <= arr[0].length <= 300`
* `0 <= arr[i][j] <=`&#x20;

```java
class Solution {
    public int countSquares(int[][] A) {
        int res = 0;
        // changing A[i][j] -> max square length with lower right corner at (i,j)
        for (int i = 0; i < A.length; ++i) {
            for (int j = 0; j < A[0].length; ++j) {
                if (A[i][j] > 0 && i > 0 && j > 0)
                    A[i][j] = Math.min(A[i - 1][j - 1], Math.min(A[i - 1][j], A[i][j - 1])) + 1;
                // lets say max len here is ->2 then we will increase count by 2
                // 1 for 2 len sq and 1 for 1 len sq
                res += A[i][j];
            }
        }
        return res;
    }
}
```