231. Power of Two

Given an integer, write a function to determine if it is a power of two.

Example 1:

Input: 1
Output: true
Explanation: 20 = 1

Example 2:

Input: 16
Output: true
Explanation: 24 = 16

Example 3:

Input: 218
Output: false

class Solution {
    public boolean isPowerOfTwo(int n) {
        boolean res = false;
        int tmp = 0;

        for(int i = 0; i < Integer.SIZE; i++){
            if(((n>>i) & 1) == 1) tmp++;
        }
        return (n > 0) && tmp == 1;
    }
}

class Solution {
    public boolean isPowerOfTwo(int n) {
        return (n>0) && ((n&(n-1)) == 0);
    }
}

真就一行啊，举例：8 == 1000, 8 - 1 = 7 == 0111，做与必定为0。

class Solution {
    public boolean isPowerOfTwo(int n) {
        return Math.log10(n) / Math.log10(2) % 1 == 0;
    }
}

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