231. Power of Two

Question

Given an integer n, return true if it is a power of two. Otherwise, return false.

An integer n is a power of two, if there exists an integer x such that n == 2x.

Algorithm

• Utilize bit manipulation.
• if a number is a power of 2, all its digits are 0 except leading 1.
• So there are actually two ways to use this attribute"
  • minus 1, all the bits would be flipped and you could use & to see if the result is 0(each filp would be different)
  • -x, −x is the same as ~x + 1, This operation reverts all bits of x except the rightmost 1-bit.if it's a power of 2, x & -x would equals x.

Code

class Solution {
    public boolean isPowerOfTwo(int n) {
        if (n == 0) return false;
        long x = (long) n;
        return (x & x - 1) == 0;
    }
}