문제 설명

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

문제풀이

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

참고 : https://leetcode.com/problems/count-square-submatrices-with-all-ones/