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Question

Original Question: Leetcode 1277. 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.

Solution

class Solution {
    public int countSquares(int[][] A) {
        int res = 0;
        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;
                }
                res += A[i][j];
            }
        }
        return res;
    }
}