# Merge two sorted linked list without duplicates

Merge two sorted linked list of size n1 and n2. The duplicates in two linked list should be present only once in the final sorted linked list.

Examples:

```Input : list1: 1->1->4->5->7
list2: 2->4->7->9
Output : 1 2 4 5 7 9
```

Approach: Following are the steps:

1. Merge the two sorted linked list in sorted manner. Refer recursive approach of this post. Let the final obtained list be head.

 `// C++ implementation to merge two sorted linked list ` `// without duplicates ` `#include ` ` `  `using` `namespace` `std; ` ` `  `// structure of a node ` `struct` `Node { ` `    ``int` `data; ` `    ``Node* next; ` `}; ` ` `  `// function to get a new node ` `Node* getNode(``int` `data) ` `{ ` `    ``// allocate space ` `    ``Node* temp = (Node*)``malloc``(``sizeof``(Node)); ` ` `  `    ``// put in data ` `    ``temp->data = data; ` `    ``temp->next = NULL; ` `    ``return` `temp; ` `} ` ` `  `// function to merge two sorted linked list ` `// in a sorted manner ` `Node* sortedMerge(``struct` `Node* a, ``struct` `Node* b) ` `{ ` `    ``Node* result = NULL; ` ` `  `    ``/* Base cases */` `    ``if` `(a == NULL) ` `        ``return` `(b); ` `    ``else` `if` `(b == NULL) ` `        ``return` `(a); ` ` `  `    ``/* Pick either a or b, and recur */` `    ``if` `(a->data <= b->data) { ` `        ``result = a; ` `        ``result->next = sortedMerge(a->next, b); ` `    ``} ` `    ``else` `{ ` `        ``result = b; ` `        ``result->next = sortedMerge(a, b->next); ` `    ``} ` `    ``return` `(result); ` `} ` ` `  `/* The function removes duplicates from a sorted list */` `void` `removeDuplicates(Node* head) ` `{ ` `    ``/* Pointer to traverse the linked list */` `    ``Node* current = head; ` ` `  `    ``/* Pointer to store the next pointer of a node to be deleted*/` `    ``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; ` `        ``} ` `        ``else` `/* This is tricky: only advance if no deletion */` `        ``{ ` `            ``current = current->next; ` `        ``} ` `    ``} ` `} ` ` `  `// function to merge two sorted linked list ` `// without duplicates ` `Node* sortedMergeWithoutDuplicates(Node* head1, Node* head2) ` `{ ` `    ``// merge two linked list in sorted manner ` `    ``Node* head = sortedMerge(head1, head2); ` ` `  `    ``// remove duplicates from the list 'head' ` `    ``removeDuplicates(head); ` ` `  `    ``return` `head; ` `} ` ` `  `// function to print the linked list ` `void` `printList(Node* head) ` `{ ` `    ``while` `(head != NULL) { ` `        ``cout << head->data << ``" "``; ` `        ``head = head->next; ` `    ``} ` `} ` ` `  `// Driver program to test above ` `int` `main() ` `{ ` `    ``// head1: 1->1->4->5->7 ` `    ``Node* head1 = getNode(1); ` `    ``head1->next = getNode(1); ` `    ``head1->next->next = getNode(4); ` `    ``head1->next->next->next = getNode(5); ` `    ``head1->next->next->next->next = getNode(7); ` ` `  `    ``// head2: 2->4->7->9 ` `    ``Node* head2 = getNode(2); ` `    ``head2->next = getNode(4); ` `    ``head2->next->next = getNode(7); ` `    ``head2->next->next->next = getNode(9); ` ` `  `    ``Node* head3; ` ` `  `    ``head3 = sortedMergeWithoutDuplicates(head1, head2); ` ` `  `    ``printList(head3); ` ` `  `    ``return` `0; ` `} `

Output:

```1 2 4 5 7 9
```

Time complexity: O(n1 + n2).
Auxiliary Space: O(1).

Exercise: Get the final sorted linked list without duplicates in a single traversal of the two lists.

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