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Sum of all odd frequency elements in an array
  • Difficulty Level : Basic
  • Last Updated : 10 Mar, 2021

Given an array of integers containing duplicate elements. The task is to find the sum of all odd occurring elements in the given array. That is the sum of all such elements whose frequency is odd in the array.
Examples: 

Input : arr[] = {1, 1, 2, 2, 3, 3, 3}
Output : 9
The odd occurring element is 3, and it's number
of occurrence is 3. Therefore sum of all 3's in the 
array = 9.

Input : arr[] = {10, 20, 30, 40, 40}
Output : 60
Elements with odd frequency are 10, 20 and 30.
Sum = 60.

Approach:  

  • Traverse the array and use a map in C++ to store the frequency of elements of the array such that the key of map is the array element and value is its frequency in the array.
  • Then, traverse the map to find the frequency of elements and check if it is odd, if it is odd, then add this element to sum.

Below is the implementation of the above approach: 

C++




// CPP program to find the sum of all odd
// occurring elements in an array
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the sum of all odd
// occurring elements in an array
int findSum(int arr[], int N)
{
    // Store frequencies of elements
    // of the array
    unordered_map<int, int> mp;
    for (int i = 0; i < N; i++)
        mp[arr[i]]++;
 
    // variable to store sum of all
    // odd occurring elements
    int sum = 0;
 
    // loop to iterate through map
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
 
        // check if frequency is odd
        if (itr->second % 2 != 0)
            sum += (itr->first) * (itr->second);
    }
 
    return sum;
}
 
// Driver Code
int main()
{
    int arr[] = { 10, 20, 20, 10, 40, 40, 10 };
 
    int N = sizeof(arr) / sizeof(arr[0]);
 
    cout << findSum(arr, N);
 
    return 0;
}

Java




// Java program to find the sum of all odd
// occurring elements in an array
import java.util.*;
 
class GFG
{
 
// Function to find the sum of all odd
// occurring elements in an array
static int findSum(int arr[], int N)
{
    // Store frequencies of elements
    // of the array
    Map<Integer,Integer> mp = new HashMap<>();
    for (int i = 0; i < N; i++)
        mp.put(arr[i],mp.get(arr[i])==null?1:mp.get(arr[i])+1);
 
    // variable to store sum of all
    // odd occurring elements
    int sum = 0;
 
    // loop to iterate through map
    for (Map.Entry<Integer,Integer> entry : mp.entrySet())
    {
 
        // check if frequency is odd
        if (entry.getValue() % 2 != 0)
            sum += (entry.getKey()) * (entry.getValue());
    }
 
    return sum;
}
 
// Driver Code
public static void main(String args[])
{
    int arr[] = { 10, 20, 20, 10, 40, 40, 10 };
 
    int N = arr.length;
 
    System.out.println(findSum(arr, N));
}
}
 
/* This code is contributed by PrinciRaj1992 */

Python3




# Function to find sum of all odd
# occurring elements in an array
import collections
 
def findsum(arr, N):
     
    # Store frequencies of elements
    # of an array in dictionary
    mp = collections.defaultdict(int)
     
    for i in range(N):
        mp[arr[i]] += 1
     
    # Variable to store sum of all
    # odd occurring elements
    sum = 0
     
    # loop to iterate through dictionary
    for i in mp:
         
        # Check if frequency is odd
        if (mp[i] % 2 != 0):
            sum += (i * mp[i])
    return sum
     
# Driver Code
arr = [ 10, 20, 20, 10, 40, 40, 10 ]
 
N = len(arr)
 
print (findsum(arr, N))
             
# This cde is contributed
# by HardeepSingh.            

C#




// C# program to find the sum of all odd
// occurring elements in an array
using System;
using System.Collections.Generic;
 
class GFG
{
    // Function to find the sum of all odd
    // occurring elements in an array
    public static int findSum(int[] arr, int N)
    {
 
        // Store frequencies of elements
        // of the array
        Dictionary<int,
                   int> mp = new Dictionary<int,       
                                            int>();
        for (int i = 0; i < N; i++)
        {
            if (mp.ContainsKey(arr[i]))
                mp[arr[i]]++;
            else
                mp.Add(arr[i], 1);
        }
 
        // variable to store sum of all
        // odd occurring elements
        int sum = 0;
 
        // loop to iterate through map
        foreach (KeyValuePair<int,
                              int> entry in mp)
        {
 
            // check if frequency is odd
            if (entry.Value % 2 != 0)
                sum += entry.Key * entry.Value;
        }
 
        return sum;
    }
 
    // Driver code
    public static void Main(String[] args)
    {
        int[] arr = { 10, 20, 20, 10, 40, 40, 10 };
        int n = arr.Length;
        Console.WriteLine(findSum(arr, n));
    }
}
 
// This code is contributed by
// sanjeev2552
Output: 
30

 

Time Complexity: O(N), where N is the number of elements in the array.
 



Method 2:Using Built in python functions:

  • Count the frequencies of every element using Counter function
  • Traverse the frequency dictionary and sum all the elements with occurrence odd frequency multiplied by its frequency.

Below is the implementation:

Python3




# Python3 implementation of the above approach
from collections import Counter
 
def sumOdd(arr, n):
 
    # Counting frequency of every
    # element using Counter
    freq = Counter(arr)
     
    # Initializing sum 0
    sum = 0
     
    # Traverse the freeq and print all
    # sum all elements with odd frequency
    # multiplieed by its frequency
    for it in freq:
        if freq[it] % 2 != 0:
            sum = sum + it*freq[it]
    print(sum)
 
 
# Driver code
arr = [10, 20, 30, 40, 40]
n = len(arr)
 
sumOdd(arr, n)
 
# This code is contributed by vikkycirus

Output:

60

Time Complexity: O(N), where N is the number of elements in the array.

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