How to Check if Given Number is Power of Two or Not | Java and Python

4 Ways to find Given Number is Power of Two or Not in Java and Python

Problem Description :

Given an integer n, return true if it is a power of two. Otherwise, return false.

An integer n is a power of two, if there exists an integer x such that n == 2x.

Example 1:

Input: n = 1
Output: true
Explanation: 20 = 1

Example 2:

Input: n = 16
Output: true
Explanation: 24 = 16

Example 3:

Input: n = 3
Output: false

Lets jump on solution. we will see 4 solutions for this problem.

Solution 1 : Check Number is Power of Two or Not using Recursive Approach in Java

import java.util.Scanner;

public class PowerOfTwo {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        
        System.out.println("Enter Number");
        int number = sc.nextInt();
        
        boolean ans = checkPowerOfTwo(number);
        System.out.println(ans);
    }

    private static boolean checkPowerOfTwo(int number) {
        if (number == 1) {
            return true;
        }
       
        if (number == 0 || number % 2 != 0) {
            return false;
        }
       
        return checkPowerOfTwo(number/2);
    }
}

Solution 2 : Check Number is Power of Two or Not using Iterative Approach

private static boolean checkPowerOfTwo(int number) {
        if (number == 0) {
            return false;
        }
       
        while (number != 1) {
            
            if (number % 2 != 0) {
                return false;
            }
            number  = number / 2;
        }
        return true;
 }

Solution 3 : Check Number is Power of Two or Not using One Line Approach

private static boolean checkPowerOfTwo(int number) {
      
        if (number <= 0) {
            return false;
        }
       
        return ((number & (number -1)) == 0);
}

Explanation :

If number equals or less than 0 then it cant be any power of 2. Now for positive numbers, it should have only one binary bit as 1.
for example,

1 -> 2^0 -> 0000001
2 -> 2^1 -> 0000010
4 -> 2^2 -> 0000100
8 -> 2^3 -> 0001000
16-> 2^4 -> 0010000
.......
.......
 

So here we can take a bitwise and (&) operation between the number and a number less than it, if it equal to 0 then it means that no other position has high bit, except at one place. Thus return true, else false.

Lets take number 32 

32  = 1 0 0 0 0 0
32 - 1 = 31 = 0 1 1 1 1 1
number & number - 1 = 0 0 0 0 0 0

&(AND) Operator returns bit by bit AND of input values example, if both bits are 1, it gives 1, else it shows 0.

Solution 4 : Check Number is Power of Two or Not in Java

private static boolean checkPowerOfTwo(int number) {
    int num = 1;
    
    while (num < n){
        num *= 2;
    }
    return num == n;  
}

Example 5 : Check Number is Power of Two or Not using BitWise Approach

private static boolean checkPowerOfTwo(int number) {
    int count=0;
    while (number > 0)  {
        if ((number & 1) == 1) {
            count++;
        }
        number  = number >> 1;
    }
    return count == 1 ? true : false;
}

Explanation : 

lets take number  = 8

Bit representation of 8 = 1 0 0 0

number >> 1 = 0 1 0 0
number >> 1 = 0 0 1 0
number >> 1 = 0 0 0 1

(1 & 1) == 1 becomes true in if condition.

Solution 6 : Check Number is Power of Two or Not using One Line in Python

class Solution(object):
    def isPowerOfTwo(self, n):
        return n > 0 and not (n & n-1)

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