Problem of the Day
A new programming or logic puzzle every Mon-Fri

Power of 2

Here's a simple one with some options for efficiency. Create a function that takes in a number and returns whether or not the number is a power of 2 or not.

Permalink: http://problemotd.com/problem/power-of-2/

Comments:

  • john smith - 10 years, 6 months ago

    java example

    I gess its simple.

    private static boolean isPower(int n) {
    if (n%2!=0)
        return false;
    if (n==2)
        return true;
    if (n%3==0 || n%5==0 || n%7==0 || n%9==0)
        return false;

    int p = 2;
    while(p<n){
        p*=2;
        if(n==p)
            return true;
    }
    return false;
}

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  • Bryan St. Amour - 10 years, 6 months ago

    In C:

    int power(int n) { return ! (n & (n - 1) ); }

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  • Nick Krichevsky - 10 years, 6 months ago

    Python

    from math import log

def log2(x):
    q=log(x,2)
    if round(q)==q:
        return True
    else:
        return False

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  • Anonymous - 10 years, 6 months ago

    #python 2.7
x = int(raw_input("Enter a number> "))
y = bin(x)
if y.count("1") == 1:
    print True
else:
    print False

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  • Ethan - 10 years, 6 months ago

    public static void checkPow(int n) {
        int pow = 1;
        for(int i = 0; i < n; i++) {
            pow *= 2;
            if(pow == n) {
                System.out.println("true");
                break;
            } else if(pow > n) {
                System.out.println("false");
                break;
            }
        }
    }

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  • Ethan - 10 years, 6 months ago

    I change my mind (thanks Nick):

    public static boolean checkPow(int n) {
    double pow = Math.log(n) / Math.log(2);
    System.out.println(pow);
    if(pow == Math.floor(pow)) {
        return true;
    } else {
        return false;
    }
}

    https://gist.github.com/eglove/5f17f098a99f3bca41eb

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  • Matthew - 10 years, 6 months ago

    Python (2 or 3): 

    def power(x): return True if bin(x).count("1")==1 else False

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  • Max Burstein - 10 years, 6 months ago

    Didn't know bin was a thing in python. Good stuff

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