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;

            }

        }

    }

};