Minimum number of operations required to delete all elements of the array

Given an integer array arr, the task is to print the minimum number of operations required to delete all elements of the array.
In an operation, any element from the array can be chosen at random and every element divisible by it can be removed from the array.

Examples:

Input: arr[] = {2, 4, 6, 3, 5, 10}
Output: 3
Choosing 2 as the first element will remove 2, 4, 6 and 10 from the array.
Now choose 3 which will result in the removal of 3.
Finally, the only element left to choose is 5.



Input: arr[] = {2, 5, 3, 7, 11}
Output: 5

Approach: For optimal results, the smallest element from the array should be chosen from the remaining elements one after another until all the elements of the array are deleted.

  • Sort the array in ascending order and prepare a hash for occurrences.
  • For each unmarked element starting from beginning mark all elements which are divisible by choose element, and increase the result counter.

Below is the implementstion of the above approach

C++

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// C++ implementation of the above approach
  
#include <bits/stdc++.h>
#define MAX 10000
  
using namespace std;
  
int hashTable[MAX];
  
// function to find minimum operations
int minOperations(int arr[], int n)
{
    // sort array
    sort(arr, arr + n);
  
    // prepare hash of array
    for (int i = 0; i < n; i++)
        hashTable[arr[i]]++;
  
    int res = 0;
    for (int i = 0; i < n; i++) {
        if (hashTable[arr[i]]) {
            for (int j = i; j < n; j++)
                if (arr[j] % arr[i] == 0)
                    hashTable[arr[j]] = 0;
            res++;
        }
    }
  
    return res;
}
  
// Driver program
int main()
{
    int arr[] = { 4, 6, 2, 8, 7, 21, 24, 49, 44 };
    int n = sizeof(arr) / sizeof(arr[0]);
  
    cout << minOperations(arr, n);
    return 0;
}

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Java

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//Java implementation of the above approach 
import java.util.*;
class Solution
{
static final int MAX=10000
  
static int hashTable[]= new int[MAX]; 
  
// function to find minimum operations 
static int minOperations(int arr[], int n) 
    // sort array 
    Arrays.sort(arr); 
  
    // prepare hash of array 
    for (int i = 0; i < n; i++) 
        hashTable[arr[i]]++; 
  
    int res = 0
    for (int i = 0; i < n; i++) { 
        if (hashTable[arr[i]]!=0) { 
            for (int j = i; j < n; j++) 
                if (arr[j] % arr[i] == 0
                    hashTable[arr[j]] = 0
            res++; 
        
    
  
    return res; 
  
// Driver program 
public static void main(String args[]) 
    int arr[] = { 4, 6, 2, 8, 7, 21, 24, 49, 44 }; 
    int n = arr.length; 
  
    System.out.print( minOperations(arr, n)); 
   
}
// This code is contributed by Arnab Kundu

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Python 3

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# Python 3 implementation of 
# the above approach
MAX = 10000
  
hashTable = [0] * MAX
  
# function to find minimum operations
def minOperations(arr, n):
      
    # sort array
    arr.sort()
  
    # prepare hash of array
    for i in range(n):
        hashTable[arr[i]] += 1
  
    res = 0
    for i in range(n) :
        if (hashTable[arr[i]]) :
            for j in range(i, n):
                if (arr[j] % arr[i] == 0):
                    hashTable[arr[j]] = 0
            res += 1
  
    return res
  
# Driver Code
if __name__ == "__main__":
    arr = [ 4, 6, 2, 8, 7, 21, 24, 49, 44 ]
    n = len(arr)
  
    print(minOperations(arr, n))
  
# This code is contributed 
# by ChitraNayal

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C#

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using System;
  
// C# implementation of the above approach  
public class Solution
{
public const int MAX = 10000;
  
public static int[] hashTable = new int[MAX];
  
// function to find minimum operations  
public static int minOperations(int[] arr, int n)
{
    // sort array  
    Array.Sort(arr);
  
    // prepare hash of array  
    for (int i = 0; i < n; i++)
    {
        hashTable[arr[i]]++;
    }
  
    int res = 0;
    for (int i = 0; i < n; i++)
    {
        if (hashTable[arr[i]] != 0)
        {
            for (int j = i; j < n; j++)
            {
                if (arr[j] % arr[i] == 0)
                {
                    hashTable[arr[j]] = 0;
                }
            }
            res++;
        }
    }
  
    return res;
}
  
// Driver program  
public static void Main(string[] args)
{
    int[] arr = new int[] {4, 6, 2, 8, 7, 21, 24, 49, 44};
    int n = arr.Length;
  
    Console.Write(minOperations(arr, n));
  
}
}
  
// This code is contributed by Shrikant13

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PHP

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<?php
// PHP implementation of the 
// above approach
  
// function to find minimum operations
function minOperations(&$arr, $n)
{
    $hashTable = array();
      
    // sort array
    sort($arr);
  
    // prepare hash of array
    for ($i = 0; $i < $n; $i++)
        $hashTable[$arr[$i]]++;
  
    $res = 0;
    for ($i = 0; $i < $n; $i++) 
    {
        if ($hashTable[$arr[$i]])
        {
            for ($j = $i; $j < $n; $j++)
                if ($arr[$j] % $arr[$i] == 0)
                    $hashTable[$arr[$j]] = 0;
            $res++;
        }
    }
  
    return $res;
}
  
// Driver Code
$arr = array(4, 6, 2, 8, 7, 21, 
                    24, 49, 44);
$n = sizeof($arr);
  
echo minOperations($arr, $n);
  
// This code is contributed 
// by Shivi_Aggarwal 
?>

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Output:

2


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