How to check if the number is a result of n^2 ?

Solution 1. Brute force

Divide number by 2 recursively and find it out.

Time complexity : O(log2n)

Solution 2. Use bitwise '&' of the number n and n-1

and check if it is equals to 0

n & (n-1) == 0

Example :

Number = 8

Binary of 8 = 1 0 0 0

Binary of 7 = 0 1 1 1

Bitwise '&' of both numbers : 0 0 0 0 = 0

Time complexity : O(1)

Example

private static boolean checkPowerOf2(int num) {

  if((num & (num-1)) == 0) {

      System.out.println(num+" is the power of 2");

  } else {

      System.out.println(num+" is not the power of 2");

  }

}