# leetcode\_1018

Given an array A of 0s and 1s, consider N\_i: the i-th subarray from A\[0] to A\[i] interpreted as a binary number (from most-significant-bit to least-significant-bit.)

Return a list of booleans answer, where answer\[i] is true if and only if N\_i is divisible by 5.

Example 1:

Input: \[0,1,1] Output: \[true,false,false] Explanation: The input numbers in binary are 0, 01, 011; which are 0, 1, and 3 in base-10. Only the first number is divisible by 5, so answer\[0] is true. Example 2:

Input: \[1,1,1] Output: \[false,false,false] Example 3:

Input: \[0,1,1,1,1,1] Output: \[true,false,false,false,true,false] Example 4:

Input: \[1,1,1,0,1] Output: \[false,false,false,false,false]

Note:

1 <= A.length <= 30000 A\[i] is 0 or 1

## Solutions

1. **math**
2. Only reverse the last digit

```cpp
class Solution {
public:
    vector<bool> prefixesDivBy5(vector<int>& A) {
        vector<bool> res;
        int n = 0;
        for (int i = 0; i < A.size(); i++) {
            n = (n << 1) | A[i];
            n = n % 10;
            res.push_back(n % 5 == 0);
        }
        return res;
    }
};
```