# Largest perfect square number in an Array

• Difficulty Level : Medium
• Last Updated : 11 Aug, 2021

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:

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## C++

 // CPP program to find the largest perfect// square number among n numbers #include#includeusing namespace std; // Function to check if a number// is perfect square number or notbool 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 arrayint 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 Codeint main(){    int a[] = { 16, 20, 25, 2, 3, 10 };     double n = sizeof(a) / sizeof(a[0]);     cout << largestPerfectSquareNumber(a, n);     return 0;}

## Java

 // Java program to find the largest perfect// square number among n numbersimport java.lang.Math;import java.io.*; class GFG {  // Function to check if a number// is perfect square number or notstatic 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 arraystatic 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 notdef 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 codeif __name__ == "__main__" :         a = [16, 20, 25, 2, 3, 10 ]    n = len(a)         print(largestPerfectSquareNumber(a, n))     # This code is contributed by Ryuga

## C#

 // C# program to find the largest perfect// square number among n numbersusing System;class GFG {  // Function to check if a number// is perfect square number or notstatic 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 arraystatic 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

 

## Javascript

 
Output:
25

Time Complexity : O()
Auxiliary Space: O(1)

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