leetcode231 2的幂 leetcode342 4的幂 leetcode326 3的幂

1.2的幂

正确写法：

class Solution {
public:
    bool isPowerOfTwo(int n) {
        if(n <= 0)
            return false;
        return (n & (n-1)) == 0;
    }
};

错误写法1：

&符号的短路原则，如果&前面为false了就不会计算后面的了

class Solution {
public:
    bool isPowerOfTwo(int n) {
        if(n <= 0)
            return false;
        retur

class Solution {
public:
    bool isPowerOfFour(int num) {
        if(num <= 0)
            return false;
        if((num & (num - 1)) == 0){
            if(num & 0x55555555)
                return true;
            else
                return false;
        }
        else
            return false;
    }
};

n ((n-1) & n) == 0;
    }
};

错误写法2

==符号的优先级比&高

class Solution {
public:
    bool isPowerOfTwo(int n) {
        if(n <= 0)
            return false;
        return n & (n-1) == 0;
    }
};

2.4的幂

class Solution {
public:
    bool isPowerOfFour(int num) {
        if(num <= 0)
            return false;
        if((num & (num - 1)) == 0){
            if(num & 0x55555555)
                return true;
            else
                return false;
        }
        else
            return false;
    }
};

3.3的幂

https://blog.csdn.net/u014218090/article/details/80152446