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