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Smallest perfect cube in an array

  • Difficulty Level : Easy
  • Last Updated : 15 Apr, 2021
Geek Week

Given an array arr[] of n integers. The task is to find the smallest perfect cube from the array. Print -1 if there is no perfect cube in the array.
Examples: 
 

Input: arr[] = {16, 8, 25, 2, 3, 10} 
Output:
8 is the only perfect cube in the array
Input: arr[] = {27, 8, 1, 64} 
Output:
All elements are perfect cubes but 1 is the minimum of all. 
 

 

A simple solution is to sort the elements and sort then numbers and start checking from start for a perfect cube number using cbrt() function. The first number from the beginning which is a perfect cube number is our answer. The complexity of sorting is O(n log n) and of cbrt() function is log n, so in 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 minimum element and store the minimum of all perfect cubes.
Below is the implementation of the above approach: 
 

C++




// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
 
// Function that returns true
// if n is a perfect cube
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 return the smallest perfect
// cube from the array
int smallestPerfectCube(int a[], int n)
{
 
    // Stores the minimum of all the
    // perfect cubes from the array
    int mini = INT_MAX;
 
    // Traverse all elements in the array
    for (int i = 0; i < n; i++) {
 
        // Store the minimum if current
        // element is a perfect cube
        if (checkPerfectcube(a[i])) {
            mini = min(a[i], mini);
        }
    }
 
    return mini;
}
 
// Driver code
int main()
{
    int a[] = { 16, 8, 25, 2, 3, 10 };
 
    int n = sizeof(a) / sizeof(a[0]);
 
    cout << smallestPerfectCube(a, n);
 
    return 0;
}

Java




// Java implementation of the approach
import java.io.*;
 
class GFG
{
 
// Function that returns true
// if n is a perfect cube
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 return the smallest perfect
// cube from the array
static int smallestPerfectCube(int a[], int n)
{
 
    // Stores the minimum of all the
    // perfect cubes from the array
    int mini = Integer.MAX_VALUE;
 
    // Traverse all elements in the array
    for (int i = 0; i < n; i++)
    {
 
        // Store the minimum if current
        // element is a perfect cube
        if (checkPerfectcube(a[i]))
        {
            mini = Math.min(a[i], mini);
        }
    }
 
    return mini;
}
 
// Driver code
public static void main (String[] args)
{
    int a[] = { 16, 8, 25, 2, 3, 10 };
 
    int n = a.length;
 
    System.out.print(smallestPerfectCube(a, n));
}
}
 
// This code is contributed by anuj_67..

Python3




# Python3 implementation of the approach
 
import sys
 
# Function that returns true
# if n is a perfect cube
def checkPerfectcube(n) :
     
    # Takes the sqrt of the number
    d = int(n**(1/3));
 
    # Checks if it is a perfect
    # cube number
    if (d * d * d == n) :
        return True;
 
    return False;
 
# Function to return the smallest perfect
# cube from the array
def smallestPerfectCube(a, n) :
 
    # Stores the minimum of all the
    # perfect cubes from the array
    mini = sys.maxsize;
 
    # Traverse all elements in the array
    for i in range(n) :
 
        # Store the minimum if current
        # element is a perfect cube
        if (checkPerfectcube(a[i])) :
            mini = min(a[i], mini);
             
    return mini;
 
 
# Driver code
if __name__ == "__main__" :
 
    a = [ 16, 8, 25, 2, 3, 10 ];
 
    n = len(a);
 
    print(smallestPerfectCube(a, n));
 
# This code is contributed by AnkitRai01

C#




// C# implementation of the approach
using System;
 
class GFG
{
 
    // Function that returns true
    // if n is a perfect cube
    static bool checkPerfectcube(int n)
    {
        // Takes the sqrt of the number
        int d = (int)Math.Sqrt(n);
     
        // Checks if it is a perfect
        // cube number
        if (d * d * d == n)
            return true;
     
        return false;
    }
     
    // Function to return the smallest perfect
    // cube from the array
    static int smallestPerfectCube(int []a, int n)
    {
     
        // Stores the minimum of all the
        // perfect cubes from the array
        int mini = int.MaxValue;
     
        // Traverse all elements in the array
        for (int i = 0; i < n; i++)
        {
     
            // Store the minimum if current
            // element is a perfect cube
            if (checkPerfectcube(a[i]))
            {
                mini = Math.Min(a[i], mini);
            }
        }
     
        return mini;
    }
     
    // Driver code
    static public void Main ()
    {
        int []a = { 16, 8, 25, 2, 3, 10 };
     
        int n = a.Length;
        Console.Write(smallestPerfectCube(a, n));
    }
}
 
// This code is contributed by ajit..

Javascript




<script>
 
// Javascript implementation of the approach
 
// Function that returns true
// if n is a perfect cube
function checkPerfectcube(n)
{
    // Takes the sqrt of the number
    let d = parseInt(Math.cbrt(n));
 
    // Checks if it is a perfect
    // cube number
    if (d * d * d == n)
        return true;
 
    return false;
}
 
// Function to return the smallest perfect
// cube from the array
function smallestPerfectCube(a, n)
{
 
    // Stores the minimum of all the
    // perfect cubes from the array
    let mini = Number.MAX_VALUE;
 
    // Traverse all elements in the array
    for (let i = 0; i < n; i++) {
 
        // Store the minimum if current
        // element is a perfect cube
        if (checkPerfectcube(a[i])) {
            mini = Math.min(a[i], mini);
        }
    }
 
    return mini;
}
 
// Driver code
let a = [ 16, 8, 25, 2, 3, 10 ];
 
let n = a.length;
 
document.write(smallestPerfectCube(a, n));
 
</script>
Output: 
8

 

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