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.

Constraints:

• 1 <= arr.length <= 300
• 1 <= arr[0].length <= 300
• 0 <= arr[i][j] <= 1

class Solution {
    public int countSquares(int[][] matrix) {
        int r = matrix.length;
        int c = r > 0 ? matrix[0].length : 0;
        if(r == 0 || c == 0) return 0;
        int res = 0;
        
        int[][] dp = new int[r+1][c+1];
        for(int i = 1; i <= r; i++){
            for(int j = 1; j <= c; j++){
                if(matrix[i-1][j-1] == 1){
                    dp[i][j] = Math.min(Math.min(dp[i-1][j-1], dp[i][j-1]), dp[i-1][j]) + 1;
                }
                if(dp[i][j] != 0) res += dp[i][j];
            }
        }
        return res;
    }
}

跟https://www.cnblogs.com/wentiliangkaihua/p/11896758.html 221.Maximal Square一毛一样，不过要注意dp数组代表几就要加几，比如3，里面也有1和2维所以要加3.否则会出现考虑情况。