LintCode-O(1) Check Power of 2

Using O(1) time to check whether an integer n is a power of 2.

Example

For n=4, return true

For n=5, return false

Challenge

O(1) time

Analysis:

Use bit manipulation. Be carefull about the 0 and negtive integer.

Solution:

class Solution {
    /*
     * @param n: An integer
     * @return: True or false
     */
    public boolean checkPowerOf2(int n) {
        if (n<=0) return false;
        boolean res = ((n & (n-1))==0) ? true : false;
        return res;
    }
};