LeetCode Daily Problem P2125 Number of Laser Beams in a Bank

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Timeline

timeline

2025-10-27

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Problem:

P2125 Number of Laser Beams in a Bank

https://leetcode.cn/problems/number-of-laser-beams-in-a-bank/description/?envType=daily-question&envId=2025-10-27

The number of laser beams is the product of the number of devices in two rows

struct Solution;

impl Solution {
    pub fn number_of_beams(bank: Vec<String>) -> i32 {
        let n = bank.len();
        let mut curr_num = 0;
        let mut first = 0;
        let mut last_num = 0;
        let mut res = 0;

        while first != n - 1 {
            if bank[first].contains('1') {
                break;
            } else {
                first += 1;
            }
        }
        if first == n {
            return 0;
        }
        last_num = bank[first].chars().filter(|&ch| ch == '1').count();

        for i in first + 1..n {
            curr_num = bank[i].chars().filter(|&ch| ch == '1').count();
            if curr_num > 0 {
                res += last_num * curr_num;
                last_num = curr_num;
            }
        }

        res as i32
    }
}