Program to find whether a number is power of 2

This post will teach you how to find whether a number is power of 2. I am using 2 types of methods to solve this problem.

Method 1 - checkPower

• If the number mod 2 not equal to 0, return false.
• Till number greater than 2, number = number/2 and check whether number mod 2 equal to 0 or not.
• If not equal to 0, return false.
• Return true at the end of loop.

Time complexity of the program is O(log n). For better results, a new method is used. It is as follows.

Method 2 - checkPower1

• Find log(number)/log(2).
• If (2^ log(number)/log(2)) equals the given number, it is power of 2. Else not.

Time complexity of the program is O(1).

The program is as follows: -

public class powerOf2 {

public static void main(String args[])

{

int num = 3;

if(checkPower(num))

{

System.out.println(" The number is a power of two");

}

else

{

System.out.println(" The number is not a power of two");

}

if(checkPower1(num))

{

System.out.println(" The number is a power of two");

}

else

{

System.out.println(" The number is not a power of two");

}

}

public static boolean checkPower(int num)

{

if(num%2!=0)

{

return false;

}

while(num>2)

{

num=num/2;

if(num%2!=0)

{

return false;

}

}

return true;

}

public static boolean checkPower1(int num)

{

double num1= (double) num;

int log = (int) (Math.log(num1)/Math.log(2));

if(Math.pow(2, log)==num1)

{ 

return true;

}

else

{

return false;

}

}

}

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