#2125
Number of Laser Beams in a Bank
pupil · 385 · lc medium +24 · verified · 87% accepted · 2,230 likes · top 98%
Description
Security devices have been activated inside a bank. You are given a 0-indexed binary string array bank representing the floor plan, which is an m x n matrix. bank[i] represents the ith row, consisting of '0's and '1's. '0' indicates an empty cell and '1' indicates a cell with a security device.
A laser beam connects two security devices when both conditions hold:
- The two devices are on different rows r1 and r2, where r1 < r2.
- Every row i between them (r1 < i < r2) contains no security devices.
Each laser beam is independent.
Return the total number of laser beams in the bank.
Example 1:
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:
* bank[0][1] -- bank[2][1]
* bank[0][1] -- bank[2][3]
* bank[0][2] -- bank[2][1]
* bank[0][2] -- bank[2][3]
* bank[0][5] -- bank[2][1]
* bank[0][5] -- bank[2][3]
* bank[2][1] -- bank[3][2]
* bank[2][3] -- bank[3][2]
Note that there is no beam between any device on the 0th row with any on the 3rd row.
This is because the 2nd row contains security devices, which breaks the second condition.
Example 2:
Input: bank = ["000","111","000"]
Output: 0
Explanation: There does not exist two devices located on two different rows.
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