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

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.

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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