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Find element in array with frequency equal to sum of frequencies of other elements
• Last Updated : 19 May, 2021

Given an integer array arr[], the task is to find an element in the array whose frequency is equal to the sum of frequencies of other elements of the array.

Examples:

Input: arr[] = {1, 2, 2, 3, 3, 3}
Output:
Explanation:
Frequencies of elements of the array –
Frequency(3) = 3
Frequency(2) = 2
Frequency(1) = 1
Here, the frequency of element 3 is equal to the
the sum of frequencies of other elements of the array.

Input: arr[] = {1, 2, 3}
Output: -1
Explanation:
In the above-given array, there is no such
element whose frequency is equal to the sum of
frequencies of other elements of the array.

Approach: The key observation in the problem is if the length of the array is odd, then there will be no such element, whereas, in the case of an even length array, calculate the frequency of each element of the array and then finally, check for any element of the array that has a frequency equal to the half-length of the array.

Below is the implementation of the above approach:

## C++

 `// C++ implementation to find the``// element whose frequency is equal``// to the sum of frequencies of``// other elements of the array` `#include ``using` `namespace` `std;` `// Function to check that any element``// have frequency equal to the sum of``// frequency of other elements of the array``bool` `isFrequencyEqual(``int` `arr[], ``int` `len)``{``    ``// Check that if the array length``    ``// is odd, Then no solution possible``    ``if` `(len % 2 == 1){``        ``cout << ``"No Such Element"``;``        ``return` `false``;``    ``}` `    ``// Hash-map to store the frequency``    ``// of elements of array``    ``map<``int``, ``int``> freq;``    ` `    ``// Loop to find the frequency``    ``// of elements of array``    ``for` `(``int` `i = 0; i < len; i++)``        ``freq[arr[i]]++;``        ` `    ``// Loop to check if any element``    ``// of the array have frequency``    ``// equal to the half length``    ``for` `(``int` `i = 0; i < len; i++){``        ``if` `(freq[arr[i]] == len / 2){``            ``cout << arr[i] << endl;``            ``return` `true``;``        ``}``    ``}``        ` `    ``cout << ``"No such element"``;``    ``return` `false``;``}` `// Driver Code``int` `main()``{``    ``int` `arr = { 1, 2, 2, 3, 3, 3 };``    ``int` `n = 6;``    ` `    ``// Function Call``    ``isFrequencyEqual(arr, n);``    ``return` `0;``}`

## Java

 `// Java implementation to find the``// element whose frequency is equal``// to the sum of frequencies of``// other elements of the array``import` `java.util.*;` `class` `GFG{`` ` `// Function to check that any element``// have frequency equal to the sum of``// frequency of other elements of the array``static` `boolean` `isFrequencyEqual(``int` `arr[], ``int` `len)``{``    ``// Check that if the array length``    ``// is odd, Then no solution possible``    ``if` `(len % ``2` `== ``1``){``        ``System.out.print(``"No Such Element"``);``        ``return` `false``;``    ``}`` ` `    ``// Hash-map to store the frequency``    ``// of elements of array``    ``HashMap freq = ``new` `HashMap();``     ` `    ``// Loop to find the frequency``    ``// of elements of array``    ``for` `(``int` `i = ``0``; i < len; i++)``        ``if``(freq.containsKey(arr[i])){``            ``freq.put(arr[i], freq.get(arr[i])+``1``);``        ``}``        ``else``{``            ``freq.put(arr[i], ``1``);``        ``}``         ` `    ``// Loop to check if any element``    ``// of the array have frequency``    ``// equal to the half length``    ``for` `(``int` `i = ``0``; i < len; i++){``        ``if` `(freq.containsKey(arr[i]) && freq.get(arr[i]) == len / ``2``){``            ``System.out.print(arr[i] +``"\n"``);``            ``return` `true``;``        ``}``    ``}``         ` `    ``System.out.print(``"No such element"``);``    ``return` `false``;``}`` ` `// Driver Code``public` `static` `void` `main(String[] args)``{``    ``int` `arr[] = { ``1``, ``2``, ``2``, ``3``, ``3``, ``3` `};``    ``int` `n = ``6``;``     ` `    ``// Function Call``    ``isFrequencyEqual(arr, n);``}``}` `// This code is contributed by Rajput-Ji`

## C#

 `// C# implementation to find the``// element whose frequency is equal``// to the sum of frequencies of``// other elements of the array``using` `System;``using` `System.Collections.Generic;` `class` `GFG{``  ` `// Function to check that any element``// have frequency equal to the sum of``// frequency of other elements of the array``static` `bool` `isFrequencyEqual(``int` `[]arr, ``int` `len)``{``    ``// Check that if the array length``    ``// is odd, Then no solution possible``    ``if` `(len % 2 == 1){``        ``Console.Write(``"No Such Element"``);``        ``return` `false``;``    ``}``  ` `    ``// Hash-map to store the frequency``    ``// of elements of array``    ``Dictionary<``int``,``int``> freq = ``new` `Dictionary<``int``,``int``>();``      ` `    ``// Loop to find the frequency``    ``// of elements of array``    ``for` `(``int` `i = 0; i < len; i++)``        ``if``(freq.ContainsKey(arr[i])){``            ``freq[arr[i]] = freq[arr[i]]+1;``        ``}``        ``else``{``            ``freq.Add(arr[i], 1);``        ``}``          ` `    ``// Loop to check if any element``    ``// of the array have frequency``    ``// equal to the half length``    ``for` `(``int` `i = 0; i < len; i++){``        ``if` `(freq.ContainsKey(arr[i]) && freq[arr[i]] == len / 2){``            ``Console.Write(arr[i] +``"\n"``);``            ``return` `true``;``        ``}``    ``}``          ` `    ``Console.Write(``"No such element"``);``    ``return` `false``;``}``  ` `// Driver Code``public` `static` `void` `Main(String[] args)``{``    ``int` `[]arr = { 1, 2, 2, 3, 3, 3 };``    ``int` `n = 6;``      ` `    ``// Function Call``    ``isFrequencyEqual(arr, n);``}``}` `// This code is contributed by Rajput-Ji`

## Python3

 `# Python3 implementation to find the``# element whose frequency is equal``# to the sum of frequencies of``# other elements of the array` `# Function to check that any element``# have frequency equal to the sum of``# frequency of other elements of the array``def` `isFrequencyEqual(arr, length) :` `    ``# Check that if the array length``    ``# is odd, Then no solution possible``    ``if` `(length ``%` `2` `=``=` `1``) :``        ``print``(``"No Such Element"``);``        ``return` `False``;` `    ``# Hash-map to store the frequency``    ``# of elements of array``    ``freq ``=` `dict``.fromkeys(arr, ``0``);``    ` `    ``# Loop to find the frequency``    ``# of elements of array``    ``for` `i ``in` `range``(length) :``        ``freq[arr[i]] ``+``=` `1``;``        ` `    ``# Loop to check if any element``    ``# of the array have frequency``    ``# equal to the half length``    ``for` `i ``in` `range``(length) :``        ``if` `(freq[arr[i]] ``=``=` `length ``/` `2``) :``            ``print``(arr[i]);``            ``return` `True``;``        ` `    ``print``(``"No such element"``,end``=``"");``    ``return` `False``;` `# Driver Code``if` `__name__ ``=``=` `"__main__"` `:` `    ``arr ``=` `[ ``1``, ``2``, ``2``, ``3``, ``3``, ``3` `];``    ``n ``=` `6``;``    ` `    ``# Function Call``    ``isFrequencyEqual(arr, n);``    ` `# This code is contributed by Yash_R`

## Javascript

 ``
Output:
`3`

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

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