Largest perfect square number in an Array

Last Updated : 17 May, 2022

Given an array of n integers. The task is to find the largest number which is a perfect square. Print -1 if there is no number that is perfect square.
Examples:

Input : arr[] = {16, 20, 25, 2, 3, 10}  Output : 25 Explanation: 25 is the largest number  that is a perfect square.   Input : arr[] = {36, 64, 10, 16, 29, 25|  Output : 64

A Simple Solution is to sort the elements and sort the n numbers and start checking from back for a perfect square number using sqrt() function. The first number from the end which is 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).
An Efficient Solution is to iterate for all the elements in O(n) and compare every time with the maximum element, and store the maximum of all perfect squares.
Below is the implementation of the above approach:

C++

// CPP program to find the largest perfect  // square number among n numbers   #include<iostream> #include<math.h> using namespace std;   // Function to check if a number  // is perfect square number or not  bool checkPerfectSquare(double n)  {      // takes the sqrt of the number      double d = sqrt(n);       // checks if it is a perfect      // square number      if (d * d == n)          return true;       return false;  }   // Function to find the largest perfect  // square number in the array  int largestPerfectSquareNumber(int a[], double n)  {      // stores the maximum of all      // perfect square numbers      int maxi = -1;       // Traverse all elements in the array      for (int i = 0; i < n; i++) {           // store the maximum if current          // element is a perfect square          if (checkPerfectSquare(a[i]))              maxi = max(a[i], maxi);      }       return maxi;  }   // Driver Code  int main()  {      int a[] = { 16, 20, 25, 2, 3, 10 };       double n = sizeof(a) / sizeof(a[0]);       cout << largestPerfectSquareNumber(a, n);       return 0;  }

// C program to find the largest perfect  // square number among n numbers  #include <stdio.h> #include <stdbool.h> #include <math.h>  int max(int a,int b) {   int max = a;   if(max < b)     max = b;   return max; }  // Function to check if a number  // is perfect square number or not  bool checkPerfectSquare(double n)  {      // takes the sqrt of the number      double d = sqrt(n);       // checks if it is a perfect      // square number      if (d * d == n)          return true;       return false;  }   // Function to find the largest perfect  // square number in the array  int largestPerfectSquareNumber(int a[], double n)  {      // stores the maximum of all      // perfect square numbers      int maxi = -1;       // Traverse all elements in the array      for (int i = 0; i < n; i++) {           // store the maximum if current          // element is a perfect square          if (checkPerfectSquare(a[i]))              maxi = max(a[i], maxi);      }       return maxi;  }   // Driver Code  int main()  {      int a[] = { 16, 20, 25, 2, 3, 10 };       double n = sizeof(a) / sizeof(a[0]);           printf("%d",largestPerfectSquareNumber(a, n));      return 0;  }   // This code is contributed by kothavvsaakash.

Java

// Java program to find the largest perfect  // square number among n numbers  import java.lang.Math;  import java.io.*;   class GFG {    // Function to check if a number  // is perfect square number or not  static boolean checkPerfectSquare(double n)  {      // takes the sqrt of the number      double d = Math.sqrt(n);       // checks if it is a perfect      // square number      if (d * d == n)          return true;       return false;  }   // Function to find the largest perfect  // square number in the array  static int largestPerfectSquareNumber(int a[], double n)  {      // stores the maximum of all      // perfect square numbers      int maxi = -1;       // Traverse all elements in the array      for (int i = 0; i < n; i++) {           // store the maximum if current          // element is a perfect square          if (checkPerfectSquare(a[i]))              maxi = Math.max(a[i], maxi);      }       return maxi;  }   // Driver Code        public static void main (String[] args) {              int []a = { 16, 20, 25, 2, 3, 10 };       double n = a.length;       System.out.println( largestPerfectSquareNumber(a, n));       }  }  // This code is contributed  // by inder_verma..

Python3

# Python3 program to find the largest perfect  # square number among n numbers  # from math lib import sqrt() from math import sqrt  # Function to check if a number   # is perfect square number or not def checkPerfectSquare(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 perfect   # square number in the array   def largestPerfectSquareNumber(a, n) :          # stores the maximum of all       # perfect square numbers      maxi = -1          # Traverse all elements in the array     for i in range(n) :                  # store the maximum if current           # element is a perfect square           if(checkPerfectSquare(a[i])) :             maxi = max(a[i], maxi)          return maxi               # Driver code if __name__ == "__main__" :          a = [16, 20, 25, 2, 3, 10 ]     n = len(a)          print(largestPerfectSquareNumber(a, n))      # This code is contributed by Ryuga

// C# program to find the largest perfect  // square number among n numbers  using System; class GFG {    // Function to check if a number  // is perfect square number or not  static bool checkPerfectSquare(double n)  {      // takes the sqrt of the number      double d = Math.Sqrt(n);       // checks if it is a perfect      // square number      if (d * d == n)          return true;       return false;  }   // Function to find the largest perfect  // square number in the array  static int largestPerfectSquareNumber(int []a, double n)  {      // stores the maximum of all      // perfect square numbers      int maxi = -1;       // Traverse all elements in the array      for (int i = 0; i < n; i++) {           // store the maximum if current          // element is a perfect square          if (checkPerfectSquare(a[i]))              maxi = Math.Max(a[i], maxi);      }       return maxi;  }   // Driver Code        public static void Main () {              int []a = { 16, 20, 25, 2, 3, 10 };       double n = a.Length;       Console.WriteLine( largestPerfectSquareNumber(a, n));       }  }  // This code is contributed  // by inder_verma..

PHP

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

JavaScript

<script>  // Javascript program to find the largest perfect  // square number among n numbers  // Function to check if a number  // is perfect square number or not  function checkPerfectSquare(n)  {      // takes the sqrt of the number      let d = Math.sqrt(n);       // checks if it is a perfect      // square number      if (d * d == n)          return true;       return false;  }   // Function to find the largest perfect  // square number in the array  function largestPerfectSquareNumber(a, n)  {      // stores the maximum of all      // perfect square numbers      let maxi = -1;       // Traverse all elements in the array      for (let i = 0; i < n; i++)     {           // store the maximum if current          // element is a perfect square          if (checkPerfectSquare(a[i]))              maxi = Math.max(a[i], maxi);      }       return maxi;  }   // Driver Code  let a = [ 16, 20, 25, 2, 3, 10 ];  let n = a.length;  document.write(largestPerfectSquareNumber(a, n));   // This code is contributed by souravmahato348. </script>

Output:

Time Complexity : O(N * \sqrt{A_i} )
Auxiliary Space: O(1)

Largest number that is not a perfect square

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Largest perfect square number in an Array

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