Find the frequencies of all duplicates elements in the array

01 Jul, 2021
Given an array of integers with duplicate elements in it, the task is to find the duplicate elements in the array and their frequencies.Examples:  
Input: arr[] = {2, 3, 4, 5, 4, 6, 4, 7, 4, 5, 6, 6} Output: Below is the frequency of repeated elements – 4 –> 4 5 –> 2 6 –> 3Input: arr[] = {4, 4, 5, 5, 6} Output: Below is the frequency of repeated elements – 4 –> 2 5 –> 2  
 
Approach:  
Create a Hash Map to store the frequency of the elements.
Elements whose frequency is greater than 1 are the repeated elements.
Below is the implementation of the above approach:  
CPP
Java
Python
C#
Javascript
// CPP Implementation to find the// repeating elements with there count#include<bits/stdc++.h>using namespace std; // Function to find the repeating// elements with there countmap<int,int> findRepeating(int arr[], int size){     // Hash map to store the    // frequency of elements    map<int,int> frequency;         // Loop to store the frequency of    // elements of array    for (int i = 0; i < size; i++)    frequency[arr[i]]++;    return frequency;}         // Driver Codeint main(){    int arr[] = {4, 4, 5, 5, 6};    int arr_size = sizeof(arr)/sizeof(arr[0]);    map<int,int> frequency = findRepeating(arr, arr_size);    cout<<"Below is the frequency of repeated elements -"<<endl;    for(auto x : frequency){        if (frequency[x.first] > 1)            cout<<x.first<<" --> "<<frequency[x.first]<<endl;    }}     // This code is contributed by Surendra_Gangwar
// Java Implementation to find the// repeating elements with there countimport java.util.*; class GFG{     // Function to find the repeating// elements with there countstatic HashMap<Integer, Integer> findRepeating(int []arr, int size){         // Hash map to store the    // frequency of elements    HashMap<Integer,Integer> frequency = new HashMap<Integer,Integer>();         // Loop to store the frequency of    // elements of array    for(int i = 0; i < size; i++)    {        if(frequency.containsKey(arr[i]))        {            frequency.put(arr[i], frequency.get(arr[i]) + 1);        }        else        {            frequency.put(arr[i], 1);        }    }    return frequency;} // Driver Codepublic static void main(String []args){    int []arr = {4, 4, 5, 5, 6};    int arr_size = arr.length;    HashMap<Integer,Integer> frequency = findRepeating(arr, arr_size);    System.out.println("Below is the frequency"    +"of repeated elements -");    for (Map.Entry<Integer,Integer> entry : frequency.entrySet())        if (entry.getValue() > 1)            System.out.println(entry.getKey()+ " --> "+entry.getValue());}} // This code is contributed by PrinciRaj1992
# Python Implementation to find the# repeating elements with there count # Function to find the repeating# elements with there countdef findRepeating(arr, size):         # Hash map to store the    # frequency of elements    frequency = {}         # Loop to store the frequency of    # elements of array    for i in range (0, size):        frequency[arr[i]] = \        frequency.get(arr[i], 0) + 1    return frequency     # Driver Codeif __name__ == "__main__":    arr = [4, 4, 5, 5, 6]    arr_size = len(arr)    frequency = findRepeating(arr, arr_size)    print("Below is the frequency\    of repeated elements -")    for i in frequency:        if frequency[i] > 1:            print(i, " --> ", frequency[i])
// C# Implementation to find the// repeating elements with there countusing System;using System.Collections.Generic; class GFG{     // Function to find the repeating// elements with there countstatic Dictionary<int, int> findRepeating(int []arr, int size){         // Hash map to store the    // frequency of elements    Dictionary<int,int> frequency = new Dictionary<int,int>();         // Loop to store the frequency of    // elements of array    for(int i = 0; i < size; i++)    {        if(frequency.ContainsKey(arr[i]))        {            frequency[arr[i]] = frequency[arr[i]] + 1;        }        else        {            frequency.Add(arr[i], 1);        }    }    return frequency;} // Driver Codepublic static void Main(String []args){    int []arr = {4, 4, 5, 5, 6};    int arr_size = arr.Length;    Dictionary<int,int> frequency = findRepeating(arr, arr_size);    Console.WriteLine("Below is the frequency"                        +"of repeated elements -");    foreach (KeyValuePair<int,int> entry in frequency)        if (entry.Value > 1)            Console.WriteLine(entry.Key+ " --> "+entry.Value);}} // This code is contributed by 29AjayKumar
<script>// Javascript Implementation to find the// repeating elements with there count     // Function to find the repeating// elements with there countfunction findRepeating(arr, size){         // Hash map to store the    // frequency of elements    var frequency = new Map();         // Loop to store the frequency of    // elements of array    for(var i = 0; i < size; i++)    {        if(frequency.has(arr[i]))        {            frequency.set(arr[i], frequency.get(arr[i])+1);        }        else        {            frequency.set(arr[i], 1);        }    }    return frequency;} // Driver Codevar arr = [4, 4, 5, 5, 6];var arr_size = arr.length;var frequency = findRepeating(arr, arr_size);document.write("Below is the frequency"                    +"of repeated elements -<br>");frequency.forEach((value, key) => {    if (value > 1)        document.write(key+ " --> "+value + "<br>");}); // This code is contributed by rrrtnx.</script>
Below is the frequency    of repeated elements -
4  -->  2
5  -->  2
 
princiraj1992
29AjayKumar
SURENDRA_GANGWAR
rrrtnx
Arrays
Hash
Arrays
Hash
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