Write a function that takes a list sorted in non-decreasing order and deletes any duplicate nodes from the list. The list should only be traversed once.
For example if the linked list is 11->11->11->21->43->43->60 then removeDuplicates() should convert the list to 11->21->43->60.
Algorithm:
Traverse the list from the head (or start) node. While traversing, compare each node with its next node. If the data of the next node is the same as the current node then delete the next node. Before we delete a node, we need to store the next pointer of the node
Implementation:
Functions other than removeDuplicates() are just to create a linked list and test removeDuplicates().
C
// C Program to remove duplicates // from a sorted linked list #include<stdio.h>#include<stdlib.h>// Link list nodestruct Node{ int data; struct Node* next;};// The function removes duplicates // from a sorted list void removeDuplicates(struct Node* head){ // Pointer to traverse the linked list struct Node* current = head; // Pointer to store the next pointer // of a node to be deleted struct Node* next_next; // Do nothing if the list is empty if (current == NULL) return; // Traverse the list till last node while (current->next != NULL) { // Compare current node with next node if (current->data == current->next->data) { // The sequence of steps is important next_next = current->next->next; free(current->next); current->next = next_next; } // This is tricky: only advance // if no deletion else { current = current->next; } }}// UTILITY FUNCTIONS // Function to insert a node at the// beginning of the linked list void push(struct Node** head_ref, int new_data){ // Allocate node struct Node* new_node = (struct Node*) malloc(sizeof(struct Node)); // Put in the data new_node->data = new_data; // Link the old list of the new node new_node->next = (*head_ref); // Move the head to point to the // new node (*head_ref) = new_node;}// Function to print nodes in a given // linked list void printList(struct Node *node){ while (node!=NULL) { printf("%d ", node->data); node = node->next; }} // Driver codeint main(){ // Start with the empty list struct Node* head = NULL; /* Let us create a sorted linked list to test the functions. Created linked list will be 11->11->11->13->13->20 */ push(&head, 20); push(&head, 13); push(&head, 13); push(&head, 11); push(&head, 11); push(&head, 11); printf( "Linked list before duplicate removal "); printList(head); // Remove duplicates from linked list removeDuplicates(head); printf( "Linked list after duplicate removal "); printList(head); return 0;} |
Output:
Linked list before duplicate removal 11 11 11 13 13 20 Linked list after duplicate removal 11 13 20
Time Complexity: O(n) where n is the number of nodes in the given linked list.
Auxiliary Space: O(1)
Recursive Approach :
C
// C recursive Program to remove duplicates// from a sorted linked list#include<stdio.h>#include<stdlib.h>// Link list node struct Node{ int data; struct Node* next;};// UTILITY FUNCTIONS // Function to insert a node at // the beginning of the linked list void push(struct Node** head_ref, int new_data){ // Allocate node struct Node* new_node = (struct Node*) malloc(sizeof(struct Node)); // Put in the data new_node->data = new_data; // Link the old list of the // new node new_node->next = (*head_ref); // Move the head to point to the // new node (*head_ref) = new_node;}// Function to print nodes in a // given linked list void printList(struct Node *node){ while (node!=NULL) { printf("%d ", node->data); node = node->next; }} Node* deleteDuplicates(Node* head) { if (head == nullptr) return nullptr; if (head->next == nullptr) return head; if (head->data == head->next->data) { Node *tmp; // If find next element duplicate, // preserve the next pointer to be // deleted, skip it, and then delete // the stored one. Return head tmp = head->next; head->next = head->next->next; free(tmp); return deleteDuplicates(head); } else { // if doesn't find next element duplicate, leave head // and check from next element head->next = deleteDuplicates(head->next); return head; }}// Driver codeint main(){ // Start with the empty list struct Node* head = NULL; /* Let us create a sorted linked list to test the functions. Created linked list will be 11->11->11->13->13->20 */ push(&head, 20); push(&head, 13); push(&head, 13); push(&head, 11); push(&head, 11); push(&head, 11); printf( "Linked list before duplicate removal "); printList(head); // Remove duplicates from linked list head = deleteDuplicates(head); printf( "Linked list after duplicate removal "); printList(head); return 0;}// This code is contributed by Yogesh shukla |
Output:
Linked list before duplicate removal 11 11 11 13 13 20 Linked list after duplicate removal 11 13 20
Time Complexity: O(n), where n is the number of nodes in the given linked list.
Auxiliary Space: O(n), due to recursive stack where n is the number of nodes in the given linked list.
Please refer complete article on Remove duplicates from a sorted linked list for more details!
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