1018.Binary Prefix Divisible By 5

1018.Binary Prefix Divisible By 5

难度:Easy

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

因为A的长度可能到30000，远超过了int表示的32位长度，因此直接相加肯定会溢出，可以在每次遍历时，将和置为其模5的值，因为往后遍历时，前面减掉的是5的倍数，后面每移一位，和乘2，也还是5的倍数，对结果没有影响。

class Solution {
public:
    vector<bool> prefixesDivBy5(vector<int>& A) {
        vector<bool> res;
        int tmp=0;
        for(auto i:A)
        {
            tmp=(tmp*2+i)%5;
            res.push_back(! (tmp));
        }
        return res;
    }
};

执行用时 :12 ms, 在所有 C++ 提交中击败了98.04%的用户 内存消耗 :10.6 MB, 在所有 C++ 提交中击败了76.07%的用户