Given a linked list that contains some random integers from 1 to n with many duplicates. Replace each duplicate element that is present in the linked list with the values n+1, n+2, n+3 and so on(starting from left to right in the given linked list).

Examples:

Input : 1 3 1 4 4 2 1 Output : 1 3 5 4 6 2 7 Replace 2nd occurrence of 1 with 5 i.e. (4+1) 2nd occurrence of 4 with 6 i.e. (4+2) 3rd occurrence of 1 with 7 i.e. (4+3) Input : 1 1 1 4 3 2 2 Output : 1 5 6 4 3 2 7

**Approach : **

1. Traverse the linked list, store the frequencies of every number present in linked list in a map and alongwith it find the maximum integer present in linked list i.e. **maxNum**.

2. Now, traverse the linked list again and if the frequency of any number is more than 1, set its value to -1 in map on its first occurrence.

3.The reason for this is that on next occurrence of this number we will find its value -1 which means this number has occurred before, change its data with maxNum + 1 and increment maxNum.

Below is the implementation of idea.

// C++ Program to replace duplicates // in an unsorted linked list #include <bits/stdc++.h> using namespace std; /* A linked list node */ struct Node { int data; struct Node* next; }; // Utility function to create a new Node struct Node* newNode(int data) { Node* temp = new Node; temp->data = data; temp->next = NULL; return temp; } // Function to replace duplicates from a // linked list void replaceDuplicates(struct Node* head) { // map to store the frequency of numbers unordered_map<int, int> mymap; Node* temp = head; // variable to store the maximum number // in linked list int maxNum = 0; // traverse the linked list to store // the frequency of every number and // find the maximum integer while (temp) { mymap[temp->data]++; if (maxNum < temp->data) maxNum = temp->data; temp = temp->next; } // Traverse again the linked list while (head) { // Mark the node with frequency more // than 1 so that we can change the // 2nd occurence of that number if (mymap[head->data] > 1) mymap[head->data] = -1; // -1 means number has occurred // before change its value else if (mymap[head->data] == -1) head->data = ++maxNum; head = head->next; } } /* Function to print nodes in a given linked list */ void printList(struct Node* node) { while (node != NULL) { printf("%d ", node->data); node = node->next; } cout << endl; } /* Driver program to test above function */ int main() { /* The constructed linked list is: 1->3->1->4->4->2->1*/ struct Node* head = newNode(1); head->next = newNode(3); head->next->next = newNode(1); head->next->next->next = newNode(4); head->next->next->next->next = newNode(4); head->next->next->next->next-> next = newNode(2); head->next->next->next->next-> next->next = newNode(1); cout << "Linked list before replacing" << " duplicates\n"; printList(head); replaceDuplicates(head); cout << "Linked list after replacing" << " duplicates\n"; printList(head); return 0; }

Output:

Linked list before replacing duplicates 1 3 1 4 4 2 1 Linked list after replacing duplicates 1 3 5 4 6 2 7

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