Remove all duplicates in an unsorted linked list

Given an unsorted linked list, write a program to remove all the duplicate elements in the unsorted linked list


Input : 10 ->12 ->11 ->11 ->12 ->11 ->10
Output : 10 ->12 ->11

This is one of the method which uses hashing to remove the duplicates in an unsorted linked list

Time Complexity: O(n),

where n is the number of nodes in the linked list, and assuming that hash table access time is O(1)

Implementation of Removing Duplicates in a unsorted list




1. Create three pointers (ex: temp, next_next, prev), where temp pointer is to traverse the linked list,  prev pointer is to point the node behind the temp(prev always follows temp) and the next_next is to store the node that should be deleted.

2. Till the end of the lined list, if the data is duplicate
a. point the prev’s next to the temp’s next ie, prev->next= temp->next
b. we need to delete the data in temp, so store it in next_next ie, next_next = temp
c. go to the next node ie, temp = temp->next

3. if the data is not duplicate
a. point the previous node to the current node ie, prev = temp
b. move the current node to current next node ie, temp = temp->next

C++ Program

using namespace std;

struct LL
	int data;
	struct LL *next;	

map<int ,int>M;

void insertAtBeginning(struct LL **head,int num)
	struct LL *temp =new LL;
	temp->next = (*head);
	temp->data = num;

void display(struct LL**head)
	struct LL*temp=*head;
			cout<<temp->data<<" ->";
			temp=temp->next; //move to next node
		//O(number of nodes)

void deleteDuplicateUnsorted(struct LL **head)
	struct LL *temp = *head, *prev=NULL, *next_next; //prev to store previous node and next_next to store next node of the current node

	while(temp != NULL)	
		if(M[temp->data]) // if the value if already found
			prev->next = temp->next; 
		prev = temp;
		M[temp->data] = 1; //intialize with count 1
		temp = temp->next; //move ahead

int main()
	struct LL *head = NULL;
    insertAtBeginning(&head, 10);
	insertAtBeginning(&head, 11);
	insertAtBeginning(&head, 12);
	insertAtBeginning(&head, 11);
	insertAtBeginning(&head, 11);
	insertAtBeginning(&head, 12);
	insertAtBeginning(&head, 10);
 	cout<<"Current List is :-\n";
	cout<<"\n After deleting alternate nodes the list becomes \n";
	return 0;

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