O(1) Check Power of 2 - LintCode

examination questions

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

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解题代码

class Solution {
public:
    /*
    * @param n: An integer
    * @return: True or false
    */
    bool checkPowerOf2(int n) {
    
        int t;
        int b;

        if (n == 1 || n == 2){
            return true;
        }
        if (n <= 0){
            return false;
        }

        while (true){
            t = n / 2;
            b = n % 2;
            if (b == 0){
                if (t == 2){
                    return true;
                }
                else{
                    n = t;
                }
            }
            else{
                return false;
            }
        }
    }
};