Find the most frequent element K positions apart from X in given Array

Given an array nums[], and integer K and X, the task is to find the most frequent element K positions away from X in the given array.

Examples:

Input: nums = [1, 100, 200, 1, 100], K = 1, X = 1
Output: 100
Explanation: Elements 1 position apart from 1 is only 100.
So the answer is 100.

Input: nums = [2, 2, 2, 2, 3], K = 2, X = 2
Output: X = 2 occurs in indices {0, 1, 2, 3}. 
Explanation: Elements 2 position apart are at {2}, {3}, {0, 4}, {1} i.e. 2, 2, {2, 3} and 2.
So 2 occurs 4 times and 3 one time, Therefore 2 is the most frequent element.

Approach: The problem can be solved using the idea of array traversal and storing the elements K distance away from X.

Follow the steps mentioned below to solve the problem:

• Search all occurrences of X in the given array
• For each occurrence of X, store the element at distance K with its frequency in a map
• At the end, just find the element in the map with most frequency and return it.

Below is the implementation of the above approach.

C++

// C++ code to implement the approach

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

// Function to find most frequent element
int mostFrequent(vector<int>& nums,
                 int K, int X)
{
      // Take one map to store count of
    // frequent element
    map<int, int> m;
    for (int i = 0; i < nums.size() - K;
                                     i++)
        if (nums[i] == X) {
            if (m.find(nums[i + K])
                        != m.end())
                m[nums[i + K]]++;
            else
                m.insert({ nums[i + K], 1 });
            if(i - K >= 0)
                m[nums[i - K]]++;
        }

      // Initialize variable ans to store
      // most frequent element
    int ans = 0, count = 0;
    for (auto i : m) {
        if (i.second > count) {
            ans = i.first;
            count = i.second;
        }
    }

    // Return ans
    return ans;
}

// Driver code
int main()
{
    vector<int> nums = { 1, 100, 200, 1, 100 };
    int K = 1, X = 1;

    // Function call
    cout << mostFrequent(nums, K, X);
    return 0;
}

Java

// Java code to implement the approach
import java.io.*;
import java.util.HashMap;
import java.util.Map;

class GFG {

  // Function to find most frequent element
  static int mostFrequent(int[] nums,
                          int K, int X)
  {

    // Take one map to store count of
    // frequent element
    HashMap<Integer, Integer> m = new HashMap<Integer, Integer>();
    for (int i = 0; i < nums.length - K; i++)
      if (nums[i] == X) {
        if (m.containsKey(nums[i + K])){
          m.put(nums[i + K],   m.get(nums[i + K]) + 1 );
        }
        else
          m.put( nums[i + K], 1 );
        if(i - K >= 0){
          if(m.containsKey(nums[i - K]))
            m.put(nums[i - K],  m.get(nums[i - K]) + 1);
        }
      }

    // Initialize variable ans to store
    // most frequent element
    int ans = 0, count = 0;
    for (Map.Entry<Integer, Integer> e : m.entrySet()){
      if(e.getValue() > count){
        ans = e.getKey();
        count = e.getValue();
      }
    }

    // Return ans
    return ans;
  }

  // Driver code
  public static void main (String[] args) {
    int[] nums = { 1, 100, 200, 1, 100 };
    int K = 1, X = 1;

    // Function call
    System.out.print(mostFrequent(nums, K, X));
  }
}

// This code is contributed by hrithikgarg03188.

Python3

# Python3 code to implement the above approach
# function to find the most frequent element
def mostFrequent(nums, K, X):

    # a dictionary/map to store the counts of frequency
    m = dict()
    for i in range(len(nums) - K):
        if nums[i + K] in m:
            m[nums[i + K]] += 1
        else:
            m[nums[i + K]] = 1
        if (i - K >= 0):
            if (nums[i - K] in m):
                m[nums[i - K]] += 1
            else:
                m[nums[i - K]] = 1

        # initialize variable answer to store the
        # most frequent element
        ans = 0
        count = 0
        for i in m:
            if m[i] > count:
                ans = i
                count = m[i]

        # return ans
        return ans

# Driver Code
nums = [1, 100, 200, 1, 100]
K = 1
X = 1

# Function Call
print(mostFrequent(nums, K, X))

# This code is contributed by phasing17

C#

// C# code to implement the approach
using System;
using System.Collections.Generic;

class GFG {

  // Function to find most frequent element
  static int mostFrequent(int[] nums, int K, int X)
  {

    // Take one map to store count of
    // frequent element
    Dictionary<int, int> m = new Dictionary<int, int>();
    for (int i = 0; i < nums.Length - K; i++)
      if (nums[i] == X) {
        if (m.ContainsKey(nums[i + K]))
          m[nums[i + K]] = m[nums[i + K]] + 1;
        else
          m.Add(nums[i + K], 1);
        if (i - K >= 0
            && m.ContainsKey(nums[i - K])) {
          m[nums[i - K]] = m[nums[i - K]] + 1;
        }
      }

    // Initialize variable ans to store
    // most frequent element
    int ans = 0, count = 0;
    foreach(KeyValuePair<int, int> x in m)
    {
      if (x.Value > count) {
        ans = x.Key;
        count = x.Value;
      }
    }

    // Return ans
    return ans;
  }

  // Driver code
  public static void Main()
  {
    int[] nums = { 1, 100, 200, 1, 100 };
    int K = 1, X = 1;

    // Function call
    Console.Write(mostFrequent(nums, K, X));
  }
}

// This code is contributed by Samim Hossain Mondal.

Javascript

<script>
    // JavaScript code to implement the approach

    // Function to find most frequent element
    const mostFrequent = (nums, K, X) => {

        // Take one map to store count of
        // frequent element
        let m = {};
        for (let i = 0; i < nums.length - K; i++)
            if (nums[i] == X) {
                if (nums[i + K] in m)
                    m[nums[i + K]]++;
                else
                    m[nums[i + K]] = 1;
                if (i - K >= 0)
                    if (nums[i - K] in m) m[nums[i - K]]++;
                    else m[nums[i - K]] = 1;
            }

        // Initialize variable ans to store
        // most frequent element
        let ans = 0, count = 0;
        for (let i in m) {
            if (m[i] > count) {
                ans = i;
                count = m[i];
            }
        }

        // Return ans
        return ans;
    }

    // Driver code
    let nums = [1, 100, 200, 1, 100];
    let K = 1, X = 1;

    // Function call
    document.write(mostFrequent(nums, K, X));

// This code is contributed by rakeshsahni

</script>

Output

100

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