Description

Given a positive integer, check whether it has alternating bits: namely, if two adjacent bits will always have different values.

Example 1:
Input: 5
Output: True
Explanation:
The binary representation of 5 is: 101

Example 2:
Input: 7
Output: False
Explanation:
The binary representation of 7 is: 111.

Example 3:
Input: 11
Output: False
Explanation:
The binary representation of 11 is: 1011.

Example 4:
Input: 10
Output: True
Explanation:
The binary representation of 10 is: 1010.

Solution

Bit manipulation

class Solution {
    public boolean hasAlternatingBits(int n) {
        // If n has alternating bits, then (n>>1) + n must be like 111...11.
        long add = (long) n + (n >> 1) + 1;
        return (add & (add - 1)) == 0;
    }
}