Number of Laser Beams in a Bank — LeetCode 2125 Python Solution

The problem

Anti-theft security devices are activated inside a bank. You are given a 0-indexed binary string array bank representing the floor plan of the bank, which is an m x n 2D matrix.

Example

Input

bank = ["011001","000000","010100","001000"]

Output

8

Explanation

Between each of the following device pairs, there is one beam. In total, there are 8 beams:

Python solution

class Solution:
    def numberOfBeams(self, bank: List[str]) -> int:
        ans = pre = 0
        for row in bank:
            if (cur := row.count("1")) > 0:
                ans += pre * cur
                pre = cur
        return ans

Complexity

Pattern: Matrix and Grid

Treat a 2-D grid as a graph whose neighbours are the four adjacent cells. LeetCode 2125. Number of Laser Beams in a Bank is filed here because LeetCode tags it Matrix, which is the vocabulary this hub collects.

The matrix and grid guide has the Python template for the pattern and the 216 LeetCode problems that use it.

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