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.      

• ​

  ​1 <= arr.length <= 300​

  ​
• ​

  ​1 <= arr[0].length <= 300​

  ​
• ​

  ​0 <= arr[i][j] <= 1​

  ​

class Solution {
public:
    int countSquares(vector<vector<int>>& matrix) {
       if (matrix.empty() == true) {
           return 0;
       }
       int m = matrix.size(), n = matrix[0].size();
       int res = 0;
       vector<vector<int>> dp(m + 1, vector<int>(n + 1, 0));
       for (int i = 0; i < m; i++) {
           for (int j = 0; j < n; j++) {
               if (matrix[i][j] == 1) {
                   dp[i + 1][j + 1] = 1 + min({dp[i][j + 1], dp[i + 1][j], dp[i][j]});
                   res += dp[i + 1][j + 1];
               }
           }
       }
       return res;
    }
};