Largest number that is not a perfect square

Given n integers, find the largest number is not a perfect square. Print -1 if there is no number that is perfect square.

Examples:

Input : arr[] = {16, 20, 25, 2, 3, 10| 
Output : 20 
Explanation: 20 is the largest number 
that is not a perfect square 

Input : arr[] = {36, 64, 10, 16, 29, 25| 
Output : 29

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

A normal solution is to sort the elements and sort the n numbers and start checking from back for a non perfect square number using sqrt() function. The first number from the end which is not a perfect square number is our answer. The complexity of sorting is O(n log n) and of sqrt() function is log n, so at the worst case the complexity is O(n log n log n).

The efficient solution is to iterate for all the elements using traversal in O(n) and compare every time with the maximum element, and store the maximum of all non perfect squares. The number stored in maximum will be our answer.

Below is the illustration of the above approach:

CPP

// CPP program to find the largest non perfect  
// square number among n numbers 
#include <bits/stdc++.h> 
using namespace std; 
bool check(int n) 
{ 
    // takes the sqrt of the number 
    int d = sqrt(n); 
  
    // checks if it is a perfect square number 
    if (d * d == n) 
        return true; 
  
    return false; 
} 
  
// function to find the largest non perfect square number 
int largestNonPerfectSquareNumber(int a[], int n) 
{ 
    // stores the maximum of all non perfect square numbers 
    int maxi = -1; 
  
    // traverse for all elements in the array 
    for (int i = 0; i < n; i++) { 
  
        // store the maximum if not a perfect square 
        if (!check(a[i])) 
            maxi = max(a[i], maxi); 
    } 
    return maxi; 
} 
  
// driver code to check the above functions 
int main() 
{ 
    int a[] = { 16, 20, 25, 2, 3, 10 }; 
  
    int n = sizeof(a) / sizeof(a[0]); 
    // function call 
    cout << largestNonPerfectSquareNumber(a, n); 
    return 0; 
} 

Java

// Java program to find the 
// largest non perfect  
// square number among n numbers 
  
import java.io.*; 
   
class GfG{ 
       
static Boolean check(int n) 
{ 
    // takes the sqrt of the number 
    int d = (int)Math.sqrt(n); 
   
    // checks if it is a perfect square number 
    if (d * d == n) 
        return true; 
   
    return false; 
} 
   
// function to find the largest 
// non perfect square number 
static int largestNonPerfectSquareNumber(int a[], int n) 
{ 
    // stores the maximum of all 
    // non perfect square numbers 
    int maxi = -1; 
   
    // traverse for all elements in the array 
    for (int i = 0; i < n; i++) { 
   
        // store the maximum if 
        // not a perfect square 
        if (!check(a[i])) 
            maxi = Math.max(a[i], maxi); 
    } 
    return maxi; 
} 
  
    public static void main (String[] args) { 
  
        int a[] = { 16, 20, 25, 2, 3, 10 }; 
        int n = a.length; 
  
        // function call 
        System.out.println(largestNonPerfectSquareNumber(a, n)); 
    } 
} 
  
// This code is contributed by Gitanjali. 

Python3

# python program to find 
# the largest non perfect  
# square number among n numbers 
  
import math 
def check( n): 
  
    # takes the sqrt of the number 
    d = int(math.sqrt(n)) 
   
    # checks if it is a 
    # perfect square number 
    if (d * d == n): 
        return True
   
    return False
  
   
# function to find the largest 
# non perfect square number 
def largestNonPerfectSquareNumber(a, n): 
  
    # stores the maximum of all 
    # non perfect square numbers 
    maxi = -1
   
    # traverse for all elements 
    # in the array 
    for i in range(0,n): 
   
        # store the maximum if 
        # not a perfect square 
        if (check(a[i])==False): 
            maxi = max(a[i], maxi) 
      
    return maxi 
  
# driver code 
a = [ 16, 20, 25, 2, 3, 10 ] 
n= len(a) 
  
# function call 
print (largestNonPerfectSquareNumber(a, n)) 
  
# This code is contributed by Gitanjali. 

C#

// C# program to find the largest non perfect  
// square number among n numbers 
using System; 
  
class GfG { 
      
    static bool check(int n) 
    { 
          
        // takes the sqrt of the number 
        int d = (int)Math.Sqrt(n); 
      
        // checks if it is a perfect  
        // square number 
        if (d * d == n) 
            return true; 
      
        return false; 
    } 
      
    // function to find the largest 
    // non perfect square number 
    static int largestNonPerfectSquareNumber( 
                               int []a, int n) 
    { 
          
        // stores the maximum of all 
        // non perfect square numbers 
        int maxi = -1; 
      
        // traverse for all elements in  
        // the array 
        for (int i = 0; i < n; i++) { 
      
            // store the maximum if 
            // not a perfect square 
            if (!check(a[i])) 
                maxi = Math.Max(a[i], maxi); 
        } 
          
        return maxi; 
    } 
  
    // driver code to check the above functions 
    public static void Main () 
    { 
  
        int []a = { 16, 20, 25, 2, 3, 10 }; 
        int n = a.Length; 
  
        // function call 
        Console.WriteLine( 
           largestNonPerfectSquareNumber(a, n)); 
    } 
} 
  
// This code is contributed by vt_m. 

PHP

<?php 
// PHP program to find  
// the largest non perfect  
// square number among n  
// numbers 
  
function check($n) 
{ 
      
    // takes the sqrt  
    // of the number 
    $d = sqrt($n); 
  
    // checks if it is a  
    // perfect square number 
    if ($d * $d == $n) 
        return true; 
  
    return false; 
} 
  
// function to find the largest 
// non perfect square number 
function largestNonPerfectSquareNumber($a, $n) 
{ 
      
    // stores the maximum of  
    // all non perfect square 
    // numbers 
    $maxi = -1; 
  
    // traverse for all  
    // elements in the array 
    for ($i = 0; $i < $n; $i++) 
    { 
  
        // store the maximum if  
        // not a perfect square 
        if (!check($a[$i])) 
            $maxi = max($a[$i], $maxi); 
    } 
    return $maxi; 
} 
  
    // Driver Code 
    $a = array(16, 20, 25, 2, 3, 10); 
    $n = count($a); 
      
    // function call 
    echo largestNonPerfectSquareNumber($a, $n); 
  
// This code is contributed by anuj_67. 
?> 

Output:

Time complexity can be considered as O(n) as sqrt() function can be implemented in O(1) time for fixed size (32 bit or 64 bit) integers [Refer Wiki for details]

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

CPP

Java

Python3

C#

PHP

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