Count Square Submatrices with All Ones

Tested Python solution for LeetCode 1277 with 15 pytest cases. Generate a practice environment with lcpy.

LeetCode 1277, Medium. Topics: Array, Dynamic Programming, Matrix. View on LeetCode.

Generate this problem as a practice environment: tested reference solution, 15 parametrized pytest cases, and a playground notebook:

lcpy gen -n 1277   # by problem number
lcpy gen -s count_square_submatrices_with_all_ones   # by problem name

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Problem

Given a m * n matrix of ones and zeros, return how many square submatrices have all ones.

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Examples

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.

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Constraints

• 1 <= arr.length <= 300
• 1 <= arr[0].length <= 300
• 0 <= arr[i][j] <= 1

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Solution

Reference implementation from solution.py on GitHub, full suite in test_solution.py:

class Solution:
    def count_squares(self, matrix: list[list[int]]) -> int:
        m, n = len(matrix), len(matrix[0])
        total = 0
        for i in range(m):
            for j in range(n):
                if matrix[i][j] and i > 0 and j > 0:
                    matrix[i][j] = 1 + min(matrix[i - 1][j], matrix[i][j - 1], matrix[i - 1][j - 1])
                total += matrix[i][j]
        return total

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Complexity

Time	Space
-	-

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Tags

NeetCode All.