342. Power of Four

标签：its   family   pow   font   orm   add   als   math   lang   

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example:
Given num = 16, return true. Given num = 5, return false.

Follow up: Could you solve it without loops/recursion?

方法1：使用换底公式，跟Power of three同理

public class Solution {
    public bool IsPowerOfFour(int num) {
        return (num > 0 && (int)(Math.Log10(num) / Math.Log10(4)) - Math.Log10(num) / Math.Log10(4) == 0);
    }
}

class Solution {
public:
    bool isPowerOfFour(int num) {
        return num > 0 && !(num & (num - 1)) && (num - 1) % 3 == 0;
    }
};

class Solution {
public:
    bool isPowerOfFour(int num) {
        return num > 0 && !(num & (num - 1)) && (num & 0x55555555) == num;
    }
};

342. Power of Four

标签：its   family   pow   font   orm   add   als   math   lang   

原文地址：http://www.cnblogs.com/xiejunzhao/p/e8f0b9357aabfe637e4d41ab0079c2c8.html