Given two linked lists, insert nodes of the second list into the first list at alternate positions of the first list.
For example, if first list is 5->7->17->13->11 and second is 12->10->2->4->6, the first list should become 5->12->7->10->17->2->13->4->11->6 and second list should become empty. The nodes of the second list should only be inserted when there are positions available. For example, if the first list is 1->2->3 and the second list is 4->5->6->7->8, then the first list should become 1->4->2->5->3->6 and the second list to 7->8.
Use of extra space is not allowed (Not allowed to create additional nodes), i.e., insertion must be done in-place. The expected time complexity is O(n) where n is the number of nodes in the first list.
The idea is to run a loop while there are available positions in first loop and insert nodes of second list by changing pointers. Following are implementations of this approach.
Java
// Java program to merge a linked list // into another at alternate positionspublic class LinkedList{ // head of list Node head; // Linked list Node class Node { int data; Node next; Node(int d) { data = d; next = null; } } /* Inserts a new Node at front of the list. */ void push(int new_data) { /* 1 & 2: Allocate the Node & Put in the data*/ Node new_node = new Node(new_data); // 3. Make next of new Node as head new_node.next = head; /* 4. Move the head to point to new Node */ head = new_node; } // Main function that inserts nodes of // linked list q into p at alternate positions. // Since head of first list never changes and // head of second list/ may change, we need single // pointer for first list and double pointer for // second list. void merge(LinkedList q) { Node p_curr = head, q_curr = q.head; Node p_next, q_next; // While there are available positions // in p; while (p_curr != null && q_curr != null) { // Save next pointers p_next = p_curr.next; q_next = q_curr.next; // make q_curr as next of p_curr // change next pointer of q_curr q_curr.next = p_next; // change next pointer of p_curr p_curr.next = q_curr; // update current pointers for // next iteration p_curr = p_next; q_curr = q_next; } q.head = q_curr; } // Function to print linked list void printList() { Node temp = head; while (temp != null) { System.out.print(temp.data + " "); temp = temp.next; } System.out.println(); } // Driver code public static void main(String args[]) { LinkedList llist1 = new LinkedList(); LinkedList llist2 = new LinkedList(); llist1.push(3); llist1.push(2); llist1.push(1); System.out.println( "First Linked List:"); llist1.printList(); llist2.push(8); llist2.push(7); llist2.push(6); llist2.push(5); llist2.push(4); System.out.println( "Second Linked List:"); llist1.merge(llist2); System.out.println( "Modified first linked list:"); llist1.printList(); System.out.println( "Modified second linked list:"); llist2.printList(); }} // This code is contributed by Rajat Mishra |
First Linked List: 1 2 3 Second Linked List: Modified first linked list: 1 4 2 5 3 6 Modified second linked list: 7 8
Time Complexity: O(N)
Auxiliary Space: O(1)
Please refer complete article on Merge linked list into another linked list at alternate positions for more details!
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