Today I have done leetcode's October LeetCoding Challenge with cpp.

October LeetCoding Challenge 27

Description

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 rows = matrix.size();
    int cols = matrix.front().size();
    int answer = 0;
    vector<vector<int>> dp(rows, vector<int>(cols));

    for(int i = 0; i < rows; ++i) {
      for(int j = 0; j < cols; ++j) {
        if(!i || !j) {
          dp[i][j] = matrix[i][j];
        } else {
          if(matrix[i][j]) {
            dp[i][j] = 1 + min({dp[i][j - 1], dp[i - 1][j], dp[i - 1][j - 1]});
          }
        }
        answer += dp[i][j];
      }
    }
    return answer;
  }
};