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Largest number in an array that is not a perfect cube
  • Difficulty Level : Basic
  • Last Updated : 22 Feb, 2021
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Given an array of n integers. The task is to find the largest number which is not a perfect cube. Print -1 if there is no number that is a perfect cube.
Examples

Input: arr[] = {16, 8, 25, 2, 3, 10} 
Output: 25
25 is the largest number that is not a perfect cube. 

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

A Simple Solution is to sort the elements and sort then numbers and start checking from back for a non-perfect cube number using cbrt() function. The first number from the end which is not a perfect cube number is our answer. The complexity of sorting is O(n log n) and of cbrt() 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 non-perfect cubes.
Below is the implementation of the above approach: 

C++




// CPP program to find the largest non-perfect
// cube number among n numbers
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to check if a number
// is perfect cube number or not
bool checkPerfectcube(int n)
{
    // takes the sqrt of the number
    int d = cbrt(n);
 
    // checks if it is a perfect
    // cube number
    if (d * d * d == n)
        return true;
 
    return false;
}
 
// Function to find the largest non perfect
// cube number in the array
int largestNonPerfectcubeNumber(int a[], int n)
{
    // stores the maximum of all
    // perfect cube 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 non perfect cube
        if (!checkPerfectcube(a[i]))
            maxi = max(a[i], maxi);
    }
 
    return maxi;
}
 
// Driver Code
int main()
{
    int a[] = { 16, 64, 25, 2, 3, 10 };
 
    int n = sizeof(a) / sizeof(a[0]);
 
    cout << largestNonPerfectcubeNumber(a, n);
 
    return 0;
}

Java




// Java program to find the largest non-perfect
// cube number among n numbers
 
import java.io.*;
 
class GFG {
   
 
// Function to check if a number
// is perfect cube number or not
static boolean checkPerfectcube(int n)
{
    // takes the sqrt of the number
    int d = (int)Math.cbrt(n);
 
    // checks if it is a perfect
    // cube number
    if (d * d * d == n)
        return true;
 
    return false;
}
 
// Function to find the largest non perfect
// cube number in the array
static int largestNonPerfectcubeNumber(int []a, int n)
{
    // stores the maximum of all
    // perfect cube 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 non perfect cube
        if (!checkPerfectcube(a[i]))
            maxi = Math.max(a[i], maxi);
    }
 
    return maxi;
}
 
// Driver Code
 
 
    public static void main (String[] args) {
    int a[] = { 16, 64, 25, 2, 3, 10 };
 
    int n = a.length;
 
    System.out.print( largestNonPerfectcubeNumber(a, n));
    }
}
// This code is contributed
// by inder_verma

Python 3




# Python 3 program to find the largest
# non-perfect cube number among n numbers
import math
 
# Function to check if a number
# is perfect cube number or not
def checkPerfectcube(n):
     
    # takes the sqrt of the number
    cube_root = n ** (1./3.)
    if round(cube_root) ** 3 == n:
        return True
    else:
        return False
 
# Function to find the largest non
# perfect cube number in the array
def largestNonPerfectcubeNumber(a, n):
     
    # stores the maximum of all
    # perfect cube numbers
    maxi = -1
 
    # Traverse all elements in the array
    for i in range(0, n, 1):
         
        # store the maximum if current
        # element is a non perfect cube
        if (checkPerfectcube(a[i]) == False):
            maxi = max(a[i], maxi)
     
    return maxi
 
# Driver Code
if __name__ == '__main__':
    a = [16, 64, 25, 2, 3, 10]
 
    n = len(a)
 
    print(largestNonPerfectcubeNumber(a, n))
 
# This code is contributed by
# Surendra_Gangwar

C#




// C# program to find the largest non-perfect
// cube number among n numbers
using System;
public class GFG {
 
 
    // Function to check if a number
    // is perfect cube number or not
    static bool checkPerfectcube(int n)
    {
        // takes the sqrt of the number
        int d = (int)Math.Ceiling(Math.Pow(n, (double)1 / 3));
 
        // checks if it is a perfect
        // cube number
        if (d * d * d == n)
            return true;
 
        return false;
    }
 
    // Function to find the largest non perfect
    // cube number in the array
    static int largestNonPerfectcubeNumber(int []a, int n)
    {
        // stores the maximum of all
        // perfect cube 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 non perfect cube
            if (checkPerfectcube(a[i])==false)
                maxi = Math.Max(a[i], maxi);
        }
 
        return maxi;
    }
 
    // Driver Code
 
 
        public static void Main () {
        int []a = { 16, 64, 25, 2, 3, 10 };
 
        int n = a.Length;
 
        Console.WriteLine( largestNonPerfectcubeNumber(a, n));
        }
}
/*This code is contributed by PrinciRaj1992*/

PHP




<?php
// PHP program to find the largest non-perfect
// cube number among n numbers
 
 
// Function to check if a number
// is perfect cube number or not
function checkPerfectcube($n)
{
    // takes the sqrt of the number
    $d = (int)round(pow($n, 1/3));
    // checks if it is a perfect
    // cube number
    if ($d * $d * $d == $n)
        return true;
 
    return false;
}
 
// Function to find the largest non perfect
// cube number in the array
function largestNonPerfectcubeNumber($a, $n)
{
    // stores the maximum of all
    // perfect cube numbers
    $maxi = -1;
 
    // Traverse all elements in the array
    for ($i = 0; $i < $n; $i++) {
 
        // store the maximum if current
        // element is a non perfect cube
        if (!checkPerfectcube($a[$i]))
            $maxi = max($a[$i], $maxi);
    }
 
    return $maxi;
}
 
// Driver Code
 
    $a = array( 16, 64, 25, 2, 3, 10 );
 
    $n = count($a);
 
    echo largestNonPerfectcubeNumber($a, $n);
 
 
// this code is contributed by mits
?>
Output: 
25

 

Time Complexity : O(n)

Auxiliary Space: O(1)

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