LeetCode_1277_Count_Square_Submatrices_with_All_Ones.cpp

/*
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.
 
  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.
*/

int countSquares(vector<vector<int>>& matrix) {
  int m = matrix.size(), n = matrix[0].size();
  vector<vector<int>> dp(m, vector<int>(n,0 ) );

  int result = 0;
  for( int i = 0; i < m; i++ )
    for( int j = 0; j < n; j++ ) {
      if( i == 0 || j == 0 ) {
	dp[i][j] = matrix[i][j];
      } else if( matrix[i][j] == 1 ) {
	dp[i][j] = min(dp[i - 1][j], min( dp[i - 1][j - 1], dp[i][j - 1] ) ) + 1;
      }
      result += dp[i][j];
    }

  return result;
}