Check whether the given number is a perfect square

Objec­tive:  Given an integer check whether it is a perfect square.


number = 37
Output: false

number = 49
Output: true

This is fun puzzle which is asked in the interview.

  1. Say number is n.
  2. Start a loop from 1 to n/2.
  3. During iteration, for every integer ‘i’, calculate x = i*i.
  4. Now with this ‘x’ there are 3 possibilities.
    1. If x == n then n is a perfect square, return true
    2. If x > n then x has crossed the n, n is not perfect square. Return false
    3. If above step a or b are not true then continue.

Time Complexity: O(sqrt(n))


public class ValidateSquare {
public static boolean isSquare(int n){
if(n==0 || n==1)
return true;
for (int i = 0; i <=n/2 ; i++) {
int x = i*i;
return true;
else if (n<x)
return false;
return false;
public static void main(String[] args) {
int n = 37;
System.out.println(n + " is square: " + isSquare(n));
n = 49;
System.out.println(n + " is square: " + isSquare(n));

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37 is square: false
49 is square: true

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