Find the index of the element in an array which divides most elements before it

Given an array arr, the task is to find the index of the element in an array which divides most elements before it
Examples:

Input: arr = {5, 2, 1, 4, 5, 8, 2}
Output: 6
Explanation
arr[6] = 2 
it divides 2, 4, and 8 (3 elements)

Input: arr = {8, 1, 28, 4, 1, 6, 7}
Output: 4

Approach:

• Maintain a map.
• For each arr[i] update the count variable by looking into map for ar[i] and insert all divisor of ar[i] into map.
• Update maxElement if cnt > maxx.
• Finally return the index with maxElement.

Below is the implementation of above approach: 

CPP

// C++ program find the index of the element
// in an array which divides
// most elements before it

#include <bits/stdc++.h>
using namespace std;

// Function to get the max element
// divisible by arr[i]
int maxElement(int arr[], int n)
{

    map<int, int> mp;
    int maxx = -1, maxElement = -1;

    for (int i = 0; i < n; i++) {
        int num = arr[i];
        int cnt = 0;

        // Update count for A[i]
        if (mp.find(num) != mp.end()) {
            cnt += mp[num];
        }

        // Generate Divisor For A[i]
        for (int j = 1; j * j <= num; j++) {
            if (num % j == 0) {
                mp[j]++;
                if (j != num / j)
                    mp[num / j]++;
            }
        }

        // Update Max Element
        if (cnt > maxx) {
            maxElement = i;
            maxx = cnt;
        }
    }

    return maxElement;
}

// Driver code
int main()
{

    int arr[] = { 5, 2, 1, 4, 5, 8, 2 };
    int n = sizeof(arr) / sizeof(arr[0]);

    cout << maxElement(arr, n) << '\n';

    return 0;
}

Java

// Java program find the index of the element
// in an array which divides
// most elements before it
import java.util.*;

class GFG
{

    // Function to get the max element
    // divisible by arr[i]
    static int maxElement(int arr[], int n)
    {

        HashMap<Integer, Integer> mp = new HashMap<Integer, Integer>();
        int maxx = -1, maxElement = -1;

        for (int i = 0; i < n; i++)
        {
            int num = arr[i];
            int cnt = 0;

            // Update count for A[i]
            if (mp.containsKey(num))
            {
                cnt += mp.get(num);
            }

            // Generate Divisor For A[i]
            for (int j = 1; j * j <= num; j++)
            {
                if (num % j == 0)
                {
                    if (mp.containsKey(j))
                        mp.put(j, mp.get(j) + 1);
                    else
                        mp.put(j, 1);
                    if (j != num / j)
                        if (mp.containsKey(num / j))
                            mp.put(num / j, mp.get(num / j) + 1);
                        else
                            mp.put(num / j, 1);
                }
            }

            // Update Max Element
            if (cnt > maxx)
            {
                maxElement = i;
                maxx = cnt;
            }
        }

        return maxElement;
    }

    // Driver code
    public static void main(String[] args)
    {

        int arr[] = { 5, 2, 1, 4, 5, 8, 2 };
        int n = arr.length;

        System.out.print(maxElement(arr, n));
    }
}

// This code is contributed by 29AjayKumar

Python

# Python3 program find the index of the element
# in an array which divides
# most elements before it

# Function to get the max element
# divisible by arr[i]
def maxElement(arr, n):

    mp = dict()
    maxx = -1
    maxElement = -1

    for i in range(n):
        num = arr[i]
        cnt = 0

        # Update count for A[i]
        if (num in mp):
            cnt += mp[num]

        # Generate Divisor For A[i]
        j = 1

        while j * j <= num:
            if (num % j == 0):
                mp[j] = mp.get(j, 0) + 1
                if (j != num // j):
                    mp[num // j] = mp.get(num//j, 0) + 1
            j += 1

        # Update Max Element
        if (cnt > maxx):
            maxElement = i
            maxx = cnt

    return maxElement

# Driver code
arr = [5, 2, 1, 4, 5, 8, 2]
n = len(arr)

print(maxElement(arr, n))

# This code is contributed by mohit kumar 29

C#

// C# program find the index of the element
// in an array which divides
// most elements before it
using System;
using System.Collections.Generic;

class GFG
{

    // Function to get the max element
    // divisible by arr[i]
    static int maxElement(int []arr, int n)
    {

        Dictionary<int, int> mp = new Dictionary<int, int>();
        int maxx = -1, maxElement = -1;

        for (int i = 0; i < n; i++)
        {
            int num = arr[i];
            int cnt = 0;

            // Update count for A[i]
            if (mp.ContainsKey(num))
            {
                cnt += mp[num];
            }

            // Generate Divisor For A[i]
            for (int j = 1; j * j <= num; j++)
            {
                if (num % j == 0)
                {
                    if (mp.ContainsKey(j))
                        mp[j] = mp[j] + 1;
                    else
                        mp.Add(j, 1);
                    if (j != num / j)
                        if (mp.ContainsKey(num / j))
                            mp[num / j] = mp[num / j] + 1;
                        else
                            mp.Add(num / j, 1);
                }
            }

            // Update Max Element
            if (cnt > maxx)
            {
                maxElement = i;
                maxx = cnt;
            }
        }

        return maxElement;
    }

    // Driver code
    public static void Main(String[] args)
    {

        int []arr = { 5, 2, 1, 4, 5, 8, 2 };
        int n = arr.Length;

        Console.Write(maxElement(arr, n));
    }
}

// This code is contributed by PrinciRaj1992

Javascript

<script>
      // JavaScript program find the index of the element
      // in an array which divides
      // most elements before it
      // Function to get the max element
      // divisible by arr[i]
      function maxElement(arr, n) {
        var mp = {};
        var maxx = -1,
          maxElement = -1;

        for (var i = 0; i < n; i++) {
          var num = arr[i];
          var cnt = 0;

          // Update count for A[i]
          if (mp.hasOwnProperty(num)) {
            cnt += mp[num];
          }

          // Generate Divisor For A[i]
          for (var j = 1; j * j <= num; j++) {
            if (num % j === 0) {
              if (mp.hasOwnProperty(j)) mp[j] = mp[j] + 1;
              else mp[j] = 1;
              if (j !== num / j)
                if (mp.hasOwnProperty(num / j)) mp[num / j] = mp[num / j] + 1;
                else mp[num / j] = 1;
            }
          }

          // Update Max Element
          if (cnt > maxx) {
            maxElement = i;
            maxx = cnt;
          }
        }

        return maxElement;
      }

      // Driver code
      var arr = [5, 2, 1, 4, 5, 8, 2];
      var n = arr.length;

      document.write(maxElement(arr, n));

      // This code is contributed by rdtank.
    </script>

Output:

6

Time Complexity: O(N?max(Arr))
 Auxiliary Space: O(N) due to map data structure.