Thinking process

What numbers are power of 2?

• 0? false
• negative? false
• 1? true
• 2? true
• 6? false
• 8? false

What are those bits look lie?

• 2 => 10
• 4 => 100
• They all have only one bit that is 1

=>Count number of 1 bits

Mistakes

6 is not power of 2, so you can't repeatedly minus 2 and check whether it's equal to 0 at last

public class Solution {
    public boolean isPowerOfTwo(int n) {
        if (n <= 0) return false;
        int res = 0;
        for (int i = 0; i < 32; ++i) {
            if ((n & (1 << i)) != 0) res++;
            if (res > 1) return false;
        }

        return true;
    }
}

Trick of n and n - 1

public class Solution {
    public boolean isPowerOfTwo(int n) {
        return (n > 0 && (n & (n - 1)) == 0);
    }
}