leetcode 342. Power of Four

最新推荐文章于 2024-06-04 11:17:38 发布

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本文介绍了一种不使用循环或递归的方法来判断一个32位带符号整数是否为4的幂。提供了两种解决方案：一种利用对数函数进行检查，另一种采用位操作实现更高效的检测。

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?

和前面2和3的情况有些类似，使用了log10，不过好像有点慢

public class Solution {
    public boolean isPowerOfFour(int num) {
        return (Math.log10(num) / Math.log10(4))%1==0;
    }
}

其他方法

public boolean isPowerOfFour(int num) {
        return num > 0 && (num&(num-1)) == 0 && (num & 0x55555555) != 0;
        //0x55555555 is to get rid of those power of 2 but not power of 4
        //so that the single 1 bit always appears at the odd position 
    }