27_Number_of_Laser_Beams_in_a_Bank.cpp

// 2125. Number of Laser Beams in a Bank

// 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. bank[i] represents the ith row, consisting of '0's and '1's. '0' means the cell is empty, while'1' means the cell has a security device.

// There is one laser beam between any two security devices if both conditions are met:

// The two devices are located on two different rows: r1 and r2, where r1 < r2.
// For each row i where r1 < i < r2, there are no security devices in the ith row.
// Laser beams are independent, i.e., one beam does not interfere nor join with another.

// 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.
 

// Constraints:

// m == bank.length
// n == bank[i].length
// 1 <= m, n <= 500
// bank[i][j] is either '0' or '1'.

class Solution
{
public:
    int numberOfBeams(vector<string> &bank)
    {
        int ans = 0, prev = 0;
        for (auto &row : bank)
        {
            int device = count(row.begin(), row.end(), '1');
            if (device > 0)
            {
                ans += device * prev;
                prev = device;
            }
        }
        return ans;
    }
};