題目

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

題目大意

給定由若干 0 和 1 組成的數組 A。我們定義 N_i：從 A[0] 到 A[i] 的第 i 個子數組被解釋為一個二進制數（從最高有效位到最低有效位）。返回布爾值列表 answer，只有當 N_i 可以被 5 整除時，答案 answer[i] 為 true，否則為 false。

解題思路

• 簡單題。每掃描數組中的一個數字，累計轉換成二進制數對 5 取餘，如果餘數為 0，則存入 true，否則存入 false。

參考代碼

package leetcode

func prefixesDivBy5(a []int) []bool {
	res, num := make([]bool, len(a)), 0
	for i, v := range a {
		num = (num<<1 | v) % 5
		res[i] = num == 0
	}
	return res
}