1277. Count Square Submatrices with All Ones.cpp

#MayChallenge
/*
Link: https://leetcode.com/problems/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
*/

// Solution

class Solution {
public:
    int countSquares(vector<vector<int>>& matrix) {
        int r = matrix.size();
        
        if(r == 0)
            return 0;
        
        int c = matrix[0].size();
        int ans = 0;
        for(int i = 0; i < r; i++) {
            for(int j = 0; j < c; j++) {
                if (matrix[i][j] == 0)
                    continue;
                ans++;
                if (i == 0 || j == 0)
                    continue;
                
                matrix[i][j] += min (matrix[i - 1][j - 1], min(matrix[i - 1][j], matrix[i][j - 1]));
                ans += matrix[i][j];
            }
        }
        return ans;
    }
};