Program to find whether a no is power of two

Given a positive integer, write a function to find if it is a power of two or not.
Examples : 

Input : n = 4
Output : Yes
22 = 4

Input : n = 7
Output : No

Input : n = 32
Output : Yes
25 = 32

1. A simple method for this is to simply take the log of the number on base 2 and if you get an integer then the number is the power of 

C++

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// C++ Program to find whether a
// no is power of two
#include<bits/stdc++.h>
using namespace std;
 
// Function to check if x is power of 2
bool isPowerOfTwo(int n)
{
   if(n==0)
   return false;
 
   return (ceil(log2(n)) == floor(log2(n)));
}
 
// Driver program
int main()
{
    isPowerOfTwo(31)? cout<<"Yes"<<endl: cout<<"No"<<endl;
    isPowerOfTwo(64)? cout<<"Yes"<<endl: cout<<"No"<<endl;
 
    return 0;
}
 
// This code is contributed by Surendra_Gangwar

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C

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// C Program to find whether a
// no is power of two
#include<stdio.h>
#include<stdbool.h>
#include<math.h>
 
/* Function to check if x is power of 2*/
bool isPowerOfTwo(int n)
{
   if(n==0)
   return false;
 
   return (ceil(log2(n)) == floor(log2(n)));
}
 
// Driver program
int main()
{
    isPowerOfTwo(31)? printf("Yes\n"): printf("No\n");
    isPowerOfTwo(64)? printf("Yes\n"): printf("No\n");
    return 0;
}
 
// This code is contributed by bibhudhendra

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Java

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// Java Program to find whether a
// no is power of two
class GFG
{
/* Function to check if x is power of 2*/
static boolean isPowerOfTwo(int n)
{
    if(n==0)
    return false;
 
return (int)(Math.ceil((Math.log(n) / Math.log(2)))) ==
       (int)(Math.floor(((Math.log(n) / Math.log(2)))));
}
 
// Driver Code
public static void main(String[] args)
{
    if(isPowerOfTwo(31))
    System.out.println("Yes");
    else
    System.out.println("No");
     
    if(isPowerOfTwo(64))
    System.out.println("Yes");
    else
    System.out.println("No");
}
}
 
// This code is contributed by mits

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Python3

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# Python3 Program to find
# whether a no is
# power of two
import math
 
# Function to check
# Log base 2
def Log2(x):
    if x == 0:
        return false;
 
    return (math.log10(x) /
            math.log10(2));
 
# Function to check
# if x is power of 2
def isPowerOfTwo(n):
    return (math.ceil(Log2(n)) ==
            math.floor(Log2(n)));
 
# Driver Code
if(isPowerOfTwo(31)):
    print("Yes");
else:
    print("No");
 
if(isPowerOfTwo(64)):
    print("Yes");
else:
    print("No");
     
# This code is contributed
# by mits

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C#

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// C# Program to find whether
// a no is power of two
using System;
 
class GFG
{
     
/* Function to check if
   x is power of 2*/
static bool isPowerOfTwo(int n)
{
 
    if(n==0)
     return false;
 
    return (int)(Math.Ceiling((Math.Log(n) /
                               Math.Log(2)))) ==
           (int)(Math.Floor(((Math.Log(n) /
                              Math.Log(2)))));
}
 
// Driver Code
public static void Main()
{
    if(isPowerOfTwo(31))
        Console.WriteLine("Yes");
    else
        Console.WriteLine("No");
     
    if(isPowerOfTwo(64))
        Console.WriteLine("Yes");
    else
        Console.WriteLine("No");
}
}
 
// This code is contributed
// by Akanksha Rai(Abby_akku)

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<?php
// PHP Program to find
// whether a no is
// power of two
 
// Function to check
// Log base 2
function Log2($x)
{
    return (log10($x) /
            log10(2));
}
 
 
// Function to check
// if x is power of 2
function isPowerOfTwo($n)
{
    return (ceil(Log2($n)) ==
            floor(Log2($n)));
}
 
// Driver Code
if(isPowerOfTwo(31))
echo "Yes\n";
else
echo "No\n";
 
if(isPowerOfTwo(64))
echo "Yes\n";
else
echo "No\n";
     
// This code is contributed
// by Sam007
?>

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Output:  

No
Yes

2. Another solution is to keep dividing the number by two, i.e, do n = n/2 iteratively. In any iteration, if n%2 becomes non-zero and n is not 1 then n is not a power of 2. If n becomes 1 then it is a power of 2. 

C++

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#include <bits/stdc++.h>
using namespace std;
 
/* Function to check if x is power of 2*/
bool isPowerOfTwo(int n)
{
    if (n == 0)
        return 0;
    while (n != 1)
    {
        if (n%2 != 0)
            return 0;
        n = n/2;
    }
    return 1;
}
 
/*Driver code*/
int main()
{
    isPowerOfTwo(31)? cout<<"Yes\n": cout<<"No\n";
    isPowerOfTwo(64)? cout<<"Yes\n": cout<<"No\n";
    return 0;
}
 
// This code is contributed by rathbhupendra

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C

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#include<stdio.h>
#include<stdbool.h>
 
/* Function to check if x is power of 2*/
bool isPowerOfTwo(int n)
{
  if (n == 0)
    return 0;
  while (n != 1)
  {
      if (n%2 != 0)
         return 0;
      n = n/2;
  }
  return 1;
}
 
/*Driver program to test above function*/
int main()
{
  isPowerOfTwo(31)? printf("Yes\n"): printf("No\n");
  isPowerOfTwo(64)? printf("Yes\n"): printf("No\n");
  return 0;
}

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// Java program to find whether
// a no is power of two
import java.io.*;
 
class GFG {
 
    // Function to check if
    // x is power of 2
    static boolean isPowerOfTwo(int n)
    {
        if (n == 0)
            return false;
         
        while (n != 1)
        {
            if (n % 2 != 0)
                return false;
            n = n / 2;
        }
        return true;
    }
 
    // Driver program
    public static void main(String args[])
    {
        if (isPowerOfTwo(31))
            System.out.println("Yes");
        else
            System.out.println("No");
 
        if (isPowerOfTwo(64))
            System.out.println("Yes");
        else
            System.out.println("No");
    }
}
 
// This code is contributed by Nikita tiwari.

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Python3

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# Python program to check if given
# number is power of 2 or not
 
# Function to check if x is power of 2
def isPowerOfTwo(n):
    if (n == 0):
        return False
    while (n != 1):
            if (n % 2 != 0):
                return False
            n = n // 2
             
    return True
 
# Driver code
if(isPowerOfTwo(31)):
    print('Yes')
else:
    print('No')
if(isPowerOfTwo(64)):
    print('Yes')
else:
    print('No')
 
# This code is contributed by Danish Raza

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C#

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// C# program to find whether
// a no is power of two
using System;
 
class GFG
{
     
    // Function to check if
    // x is power of 2
    static bool isPowerOfTwo(int n)
    {
        if (n == 0)
            return false;
         
        while (n != 1) {
            if (n % 2 != 0)
                return false;
                 
            n = n / 2;
        }
        return true;
    }
 
    // Driver program
    public static void Main()
    {
        Console.WriteLine(isPowerOfTwo(31) ? "Yes" : "No");
        Console.WriteLine(isPowerOfTwo(64) ? "Yes" : "No");
 
    }
}
 
// This code is contributed by Sam007

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<?php
 
// Function to check if
// x is power of 2
function isPowerOfTwo($n)
{
if ($n == 0)
    return 0;
while ($n != 1)
{
    if ($n % 2 != 0)
        return 0;
    $n = $n / 2;
}
return 1;
}
 
// Driver Code
if(isPowerOfTwo(31))
    echo "Yes\n";
else
    echo "No\n";
 
if(isPowerOfTwo(64))
    echo "Yes\n";
else
    echo "No\n";
 
// This code is contributed
// by Sam007
?>

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Output :  



No
Yes






3. Another way is to use this simple recursive solution. It uses the same logic as the above iterative solution but uses recursion instead of iteration. 

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// C++ program for above approach
#include <bits/stdc++.h>
using namespace std;
 
// Function which checks whether a
// number is a power of 2
bool powerOf2(int n)
{
    // base cases
    // '1' is the only odd number
    // which is a power of 2(2^0)
    if (n == 1)
      return true;
     
    // all other odd numbers are not powers of 2
    else if (n % 2 != 0 || n ==0)
      return false;
     
    // recursive function call
    return powerOf2(n / 2);
}
 
// Driver Code
int main()
{
    int n = 64;//True
    int m = 12;//False
 
    if (powerOf2(n) == 1)
      cout << "True" << endl;
 
    else cout << "False" << endl;
 
    if (powerOf2(m) == 1)
      cout << "True" << endl;
 
    else
      cout << "False" << endl;
}
 
//code contributed by Moukthik a.k.a rowdyninja

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// Java program for
// the above approach
import java.util.*;
class GFG{
 
// Function which checks
// whether a number is a
// power of 2
static boolean powerOf2(int n)
{
  // base cases
  // '1' is the only odd number
  // which is a power of 2(2^0)
  if (n == 1)
    return true;
 
  // all other odd numbers are
  // not powers of 2
  else if (n % 2 != 0 ||
           n ==0)
    return false;
 
  // recursive function call
  return powerOf2(n / 2);
}
 
// Driver Code
public static void main(String[] args)
{
  //True
  int n = 64;
   
  //False
  int m = 12;
 
  if (powerOf2(n) == true)
    System.out.print("True" + "\n");
  else System.out.print("False" + "\n");
 
  if (powerOf2(m) == true)
    System.out.print("True" + "\n");
  else
    System.out.print("False" + "\n");
}
}
 
// This code is contributed by Princi Singh

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Python3

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# Python program for above approach
 
# function which checks whether a
# number is a power of 2
def powerof2(n):
   
    # base cases
    # '1' is the only odd number
    # which is a power of 2(2^0)
    if n == 1:
        return True
     
    # all other odd numbers are not powers of 2
    elif n%2 != 0 or n == 0:
        return False
     
    #recursive function call
    return powerof2(n/2)
   
# Driver Code
if __name__ == "__main__":
   
  print(powerof2(64)) #True
  print(powerof2(12)) #False
   
#code contributed by Moukthik a.k.a rowdyninja

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// C# program for above approach
using System;
 
class GFG{
     
// Function which checks whether a
// number is a power of 2
static bool powerOf2(int n)
{
     
    // Base cases
    // '1' is the only odd number
    // which is a power of 2(2^0)
    if (n == 1)
      return true;
      
    // All other odd numbers
    // are not powers of 2
    else if (n % 2 != 0 || n == 0)
      return false;
      
    // Recursive function call
    return powerOf2(n / 2);
}
 
// Driver code
static void Main()
{
   
    int n = 64;//True
    int m = 12;//False
     
    if (powerOf2(n))
    {
        Console.Write("True" + "\n");
    }
    else
    {
        Console.Write("False" + "\n");
    }
     
    if (powerOf2(m))
    {
        Console.Write("True");
    }
    else
    {
        Console.Write("False");
    }
}
}
 
// This code is contributed by rutvik_56

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Output

True
False







4. All power of two numbers has only a one-bit set. So count the no. of set bits and if you get 1 then the number is a power of 2. Please see Count set bits in an integer for counting set bits.

5. If we subtract a power of 2 numbers by 1 then all unset bits after the only set bit become set; and the set bit becomes unset.
For example for 4 ( 100) and 16(10000), we get the following after subtracting 1 
3 –> 011 
15 –> 01111

So, if a number n is a power of 2 then bitwise & of n and n-1 will be zero. We can say n is a power of 2 or not based on the value of n&(n-1). The expression n&(n-1) will not work when n is 0. To handle this case also, our expression will become n& (!n&(n-1)) (thanks to https://www.geeksforgeeks.org/program-to-find-whether-a-no-is-power-of-two/Mohammad for adding this case). 

Below is the implementation of this method.  

C++

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#include <bits/stdc++.h>
using namespace std;
#define bool int
 
/* Function to check if x is power of 2*/
bool isPowerOfTwo (int x)
{
    /* First x in the below expression is for the case when x is 0 */
    return x && (!(x&(x-1)));
}
 
/*Driver code*/
int main()
{
    isPowerOfTwo(31)? cout<<"Yes\n": cout<<"No\n";
    isPowerOfTwo(64)? cout<<"Yes\n": cout<<"No\n";
    return 0;
}
 
// This code is contributed by rathbhupendra

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C

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#include<stdio.h>
#define bool int
 
/* Function to check if x is power of 2*/
bool isPowerOfTwo (int x)
{
  /* First x in the below expression is for the case when x is 0 */
  return x && (!(x&(x-1)));
}
 
/*Driver program to test above function*/
int main()
{
  isPowerOfTwo(31)? printf("Yes\n"): printf("No\n");
  isPowerOfTwo(64)? printf("Yes\n"): printf("No\n");
  return 0;
}

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Java

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// Java program to efficiently
// check for power for 2
 
class Test
{
    /* Method to check if x is power of 2*/
    static boolean isPowerOfTwo (int x)
    {
      /* First x in the below expression is
        for the case when x is 0 */
        return x!=0 && ((x&(x-1)) == 0);
         
    }
     
    // Driver method
    public static void main(String[] args)
    {
         System.out.println(isPowerOfTwo(31) ? "Yes" : "No");
         System.out.println(isPowerOfTwo(64) ? "Yes" : "No");
         
    }
}
// This program is contributed by Gaurav Miglani   

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# Python program to check if given
# number is power of 2 or not
 
# Function to check if x is power of 2
def isPowerOfTwo (x):
 
    # First x in the below expression
    # is for the case when x is 0
    return (x and (not(x & (x - 1))) )
 
# Driver code
if(isPowerOfTwo(31)):
    print('Yes')
else:
    print('No')
     
if(isPowerOfTwo(64)):
    print('Yes')
else:
    print('No')
     
# This code is contributed by Danish Raza   

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C#

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// C# program to efficiently
// check for power for 2
using System;
 
class GFG
{
    // Method to check if x is power of 2
    static bool isPowerOfTwo (int x)
    {
        // First x in the below expression 
        // is for the case when x is 0
        return x != 0 && ((x & (x - 1)) == 0);
         
    }
     
    // Driver method
    public static void Main()
    {
        Console.WriteLine(isPowerOfTwo(31) ? "Yes" : "No");
        Console.WriteLine(isPowerOfTwo(64) ? "Yes" : "No");
         
    }
}
 
// This code is contributed by Sam007

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PHP

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<?php
// PHP program to efficiently
// check for power for 2
 
// Function to check if
// x is power of 2
function isPowerOfTwo ($x)
{
// First x in the below expression
// is for the case when x is 0
return $x && (!($x & ($x - 1)));
}
 
// Driver Code
if(isPowerOfTwo(31))
    echo "Yes\n" ;
else
    echo "No\n";
 
if(isPowerOfTwo(64))
    echo "Yes\n" ;
else
    echo "No\n";
         
// This code is contributed by Sam007
?>

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Output :  

No
Yes






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