231. Power of Two*
https://leetcode.com/problems/power-of-two/
题目描述
Given an integer, write a function to determine if it is a power of two.
Example 1:
Input: 1
Output: true
Explanation: 20 = 1
Example 2:
Input: 16
Output: true
Explanation: 24 = 16
Example 3:
Input: 218
Output: false
C++ 实现 1
使用递归的方法实现.
class Solution {
public:
bool isPowerOfTwo(int n) {
if (n == 1) return true;
if (n % 2 == 1 || n == 0) return false;
n /= 2;
return isPowerOfTwo(n);
}
};
C++ 实现 2
使用移位的方法实现. 来自 LeetCode Submission.
class Solution {
public:
bool isPowerOfTwo(int n) {
if(n == 0) {
return false;
}
while(n != 1) {
if(n & 1) {
return false;
} else {
n >>= 1;
}
}
return true;
}
};
C++ 实现 3
Power of 2 means only one bit of n is ‘1’, so use the trick n&(n-1)==0 to judge whether that is the case
class Solution {
public:
bool isPowerOfTwo(int n) {
if(n<=0) return false;
return !(n&(n-1));
}
};