1277. Count Square Submatrices with All Ones

Problem Link

Description

---

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

---

Python3

class Solution:
    def countSquares(self, A: List[List[int]]) -> int:
        rows, cols = len(A), len(A[0])
 
        for i in range(1, rows):
            for j in range(1, cols):
                m = min(A[i - 1][j], A[i][j - 1], A[i - 1][j - 1])
 
                if A[i][j] == 1:
                    A[i][j] = m + 1 
        
        return sum(map(sum, A))