标签：
Given an integer, write a function to determine if it is a power of two.
Analyse: ***Notice that if a number is a power of 2, then the highest binary digit is 1 and the remaining digits are all 0s. So n & (n-1) = 0. If a number is not a power of 2, then n & (n - 1) != 0.
Runtime: 4ms.
class Solution {
public:
bool isPowerOfTwo(int n) {
if(n <= 0 ) return false;
return (n & (n - 1)) == 0;
}
};
Other solution:
1. Runtime: 8ms.
1 class Solution { 2 public: 3 bool isPowerOfTwo(int n) { 4 if(n <= 0 ) return false; 5 6 int remain = 1; 7 while(n != 1){ 8 remain = n % 2; 9 if(remain == 1) return false; 10 n /= 2; 11 } 12 return true; 13 } 14 };
2. Rutime: 8ms
1 class Solution { 2 public: 3 bool isPowerOfTwo(int n) { 4 if(n <= 0 ) return false; 5 6 long long num = 1; 7 while(num <= n){ 8 if(num == n) return true; 9 num <<= 1; 10 } 11 return false; 12 } 13 };
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原文地址：http://www.cnblogs.com/amazingzoe/p/4768306.html
