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Given an integer, write a function to determine if it is a power of two.
method:
1. recursive:
if x % 2 != 0, return false;
if x == 0, return false;
if x == 1, return true;
else, return isPowerOfTwo(x / 2);
1 class Solution { 2 public: 3 bool isPowerOfTwo(int n) { 4 if (n == 1) { 5 return true; 6 } 7 if (n == 0 || n % 2 != 0) { 8 return false; 9 } 10 return isPowerOfTwo(n / 2); 11 } 12 };
2. trick
if x is power of 2, there is only one ‘1‘ in x(bit format). Using x & (x - 1) calculate the count of 1 in x.
1 class Solution { 2 public: 3 bool isPowerOfTwo(int n) { 4 return n > 0 && ((n & (n - 1)) == 0); 5 } 6 };
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原文地址：http://www.cnblogs.com/huj690/p/4630965.html
