Anti-theft security devices are activated inside a bank. You are given a 0-indexed binary string array bankrepresenting the floor plan of the bank, which is an m x n2D matrix. bank[i]represents the ithrow, 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: r1and r2, where r1 < r2.

(资料图)

For each row iwhere r1 < i < r2, there are no security devices in the ithrow.

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'.

主要就是判断每一层对应的激光机器的数量；

这里用list去存储，

如果list的大小<2，那么就没有激光；

如果＞2，就是遍历每一层跟下面一层的数量，乘积最后求和，返回即可；

下面是代码：

Runtime: 12 ms, faster than 99.09% of Java online submissions for Number of Laser Beams in a Bank.

Memory Usage: 43.4 MB, less than 26.14% of Java online submissions for Number of Laser Beams in a Bank.