# Sum of all odd frequency nodes of the Linked List

Given a linked list, the task is to find the sum of all the odd frequency nodes from the given linked list.

**Examples:**

Input:8 -> 8 -> 1 -> 4 -> 1 -> 2 -> 8 -> NULL

Output:30

freq(8) = 3

freq(1) = 2

freq(4) = 1

freq(2) = 1

8, 4 and 2 appear odd number of times and (8 * 3) + (4 * 1) + (2 * 1) = 30

Input:6 -> 2 -> 2 -> 6 -> 2 -> 1 -> NULL

Output:7

**Approach:** This problem can be solved by hashing,

- Create a hash to store the frequencies of the nodes.
- Traverse the Linked List and update the frequencies of the nodes in the hash variable.
- Now, traverse the linked list again and for every node that appears odd number of times, add it’s value to the running sum.

Below is the implementation of the above approach:

## C++

`// C++ implementation of above approach ` `#include<bits/stdc++.h> ` `using` `namespace` `std; ` ` ` `// Node class ` `struct` `Node ` `{ ` ` ` `int` `data; ` ` ` `Node* next; ` ` ` `Node(` `int` `d) ` ` ` `{ ` ` ` `data = d; ` ` ` `next = NULL; ` ` ` `} ` `} ; ` ` ` `// Function to push the new node ` `// to head of the linked list ` `Node* push(Node* head,` `int` `data) ` `{ ` ` ` `// If head is null return new node as head ` ` ` `if` `(!head) ` ` ` `return` `new` `Node(data); ` ` ` `Node* temp =` `new` `Node(data); ` ` ` `temp->next = head; ` ` ` `head = temp; ` ` ` `return` `head; ` `} ` ` ` `// Function to find the sum of all odd ` `// frequency nodes of the linked list ` `int` `sumOfOddFreqEle(Node* head) ` `{ ` ` ` `// Hash to store the frequencies of ` ` ` `// the nodes of the linked list ` ` ` `map<` `int` `,` `int` `> mp ; ` ` ` `Node* temp = head; ` ` ` `while` `(temp) ` ` ` `{ ` ` ` `int` `d = temp->data; ` ` ` `mp[d]++; ` ` ` `temp = temp->next; ` ` ` `} ` ` ` ` ` `// Initialize total_sum as zero ` ` ` `int` `total_sum = 0; ` ` ` ` ` `// Traverse through the map to get the sum ` ` ` `for` `(` `auto` `i : mp) ` ` ` `{ ` ` ` ` ` `// If it appears for odd number of ` ` ` `// times then add it to the sum ` ` ` `if` `(i.second % 2 == 1) ` ` ` `total_sum+=(i.second * i.first); ` ` ` `} ` ` ` `return` `total_sum; ` `} ` ` ` `// Driver code ` `int` `main() ` `{ ` ` ` `Node* head = NULL; ` ` ` `head = push(head, 8); ` ` ` `head = push(head, 2); ` ` ` `head = push(head, 1); ` ` ` `head = push(head, 4); ` ` ` `head = push(head, 1); ` ` ` `head = push(head, 8); ` ` ` `head = push(head, 8); ` ` ` ` ` `cout<<(sumOfOddFreqEle(head)); ` ` ` ` ` `return` `0; ` `} ` ` ` `// This code is contributed by Arnab Kundu ` |

*chevron_right*

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## Python

`# Python implementation of the approach ` ` ` `# Node class ` `class` `Node: ` ` ` `def` `__init__(` `self` `, data): ` ` ` `self` `.data ` `=` `data ` ` ` `self` `.` `next` `=` `None` ` ` `# Function to push the new node ` `# to head of the linked list ` `def` `push(head, data): ` ` ` ` ` `# If head is null return new node as head ` ` ` `if` `not` `head: ` ` ` `return` `Node(data) ` ` ` `temp ` `=` `Node(data) ` ` ` `temp.` `next` `=` `head ` ` ` `head ` `=` `temp ` ` ` `return` `head ` ` ` `# Function to find the sum of all odd ` `# frequency nodes of the linked list ` `def` `sumOfOddFreqEle(head): ` ` ` ` ` `# Hash to store the frequencies of ` ` ` `# the nodes of the linked list ` ` ` `mp ` `=` `{} ` ` ` `temp ` `=` `head ` ` ` `while` `(temp): ` ` ` `d ` `=` `temp.data ` ` ` `if` `d ` `in` `mp: ` ` ` `mp[d]` `=` `mp.get(d)` `+` `1` ` ` `else` `: ` ` ` `mp[d]` `=` `1` ` ` `temp ` `=` `temp.` `next` ` ` ` ` `# Initialize total_sum as zero ` ` ` `total_sum ` `=` `0` ` ` ` ` `# Traverse through the map to get the sum ` ` ` `for` `digit ` `in` `mp: ` ` ` ` ` `# keep tracking the to ` ` ` `tms ` `=` `mp.get(digit) ` ` ` ` ` `# If it appears for odd number of ` ` ` `# times then add it to the sum ` ` ` `if` `tms ` `%` `2` `=` `=` `1` `: ` ` ` `total_sum` `+` `=` `(tms ` `*` `digit) ` ` ` `return` `total_sum ` ` ` `# Driver code ` `if` `__name__` `=` `=` `'__main__'` `: ` ` ` `head ` `=` `None` ` ` `head ` `=` `push(head, ` `8` `) ` ` ` `head ` `=` `push(head, ` `2` `) ` ` ` `head ` `=` `push(head, ` `1` `) ` ` ` `head ` `=` `push(head, ` `4` `) ` ` ` `head ` `=` `push(head, ` `1` `) ` ` ` `head ` `=` `push(head, ` `8` `) ` ` ` `head ` `=` `push(head, ` `8` `) ` ` ` ` ` `print` `(sumOfOddFreqEle(head)) ` |

*chevron_right*

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**Output:**

30

## Recommended Posts:

- Splitting starting N nodes into new Circular Linked List while preserving the old nodes
- Append odd position nodes in reverse at the end of even positioned nodes in a Linked List
- Construct a Maximum Sum Linked List out of two Sorted Linked Lists having some Common nodes
- Delete N nodes after M nodes of a linked list
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- Sum and Product of all the nodes which are less than K in the linked list
- Sum of the alternate nodes of linked list
- Linked List Product of Nodes Between 0s
- Segregate even and odd nodes in a Linked List
- Find the sum of last n nodes of the given Linked List
- Sum of all distinct nodes in a linked list

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