Java Program For Pairwise Swapping Elements Of A Given Linked List By Changing Links
Given a singly linked list, write a function to swap elements pairwise. For example, if the linked list is 1->2->3->4->5->6->7 then the function should change it to 2->1->4->3->6->5->7, and if the linked list is 1->2->3->4->5->6 then the function should change it to 2->1->4->3->6->5
This problem has been discussed here. The solution provided there swaps data of nodes. If data contains many fields, there will be many swap operations. So changing links is a better idea in general. Following is the implementation that changes links instead of swapping data.
Java
// Java program to swap elements of // linked list by changing links class LinkedList { static Node head; static class Node { int data; Node next; Node( int d) { data = d; next = null ; } } /* Function to pairwise swap elements of a linked list */ Node pairWiseSwap(Node node) { // If linked list is empty or // there is only one node in list if (node == null || node.next == null ) { return node; } // Initialize previous and // current pointers Node prev = node; Node curr = node.next; // Change head before proceeding node = curr; // Traverse the list while ( true ) { Node next = curr.next; // Change next of current as // previous node curr.next = prev; // If next NULL or next is the // last node if (next == null || next.next == null ) { prev.next = next; break ; } // Change next of previous to // next next prev.next = next.next; // Update previous and curr prev = next; curr = prev.next; } return node; } /* Function to print nodes in a given linked list */ void printList(Node node) { while (node != null ) { System.out.print(node.data + " " ); node = node.next; } } // Driver code public static void main(String[] args) { /* The constructed linked list is: 1->2->3->4->5->6->7 */ LinkedList list = new LinkedList(); list.head = new Node( 1 ); list.head.next = new Node( 2 ); list.head.next.next = new Node( 3 ); list.head.next.next.next = new Node( 4 ); list.head.next.next.next.next = new Node( 5 ); list.head.next.next.next.next.next = new Node( 6 ); list.head.next.next.next.next.next.next = new Node( 7 ); System.out.println( "Linked list before calling pairwiseSwap() " ); list.printList(head); Node st = list.pairWiseSwap(head); System.out.println( "" ); System.out.println( "Linked list after calling pairwiseSwap() " ); list.printList(st); System.out.println( "" ); } } // This code is contributed by Mayank Jaiswal |
Output:
Linked list before calling pairWiseSwap() 1 2 3 4 5 6 7 Linked list after calling pairWiseSwap() 2 1 4 3 6 5 7
Time Complexity: The time complexity of the above program is O(n) where n is the number of nodes in a given linked list. The while loop does a traversal of the given linked list.
Auxiliary Space: O(1)
Following is the recursive implementation of the same approach. We change the first two nodes and recur for the remaining list. Thanks to geek and omer salem for suggesting this method.
Java
// Java program to swap elements of // linked list by changing links class LinkedList { static Node head; static class Node { int data; Node next; Node( int d) { data = d; next = null ; } } /* Function to pairwise swap elements of a linked list. It returns head of the modified list, so return value of this node must be assigned */ Node pairWiseSwap(Node node) { // Base Case: The list is empty or // has only one node if (node == null || node.next == null ) { return node; } // Store head of list after two // nodes Node remaining = node.next.next; // Change head Node newhead = node.next; // Change next of second node node.next.next = node; // Recur for remaining list and change // next of head node.next = pairWiseSwap(remaining); // Return new head of modified list return newhead; } /* Function to print nodes in a given linked list */ void printList(Node node) { while (node != null ) { System.out.print(node.data + " " ); node = node.next; } } // Driver code public static void main(String[] args) { /* The constructed linked list is: 1->2->3->4->5->6->7 */ LinkedList list = new LinkedList(); list.head = new Node( 1 ); list.head.next = new Node( 2 ); list.head.next.next = new Node( 3 ); list.head.next.next.next = new Node( 4 ); list.head.next.next.next.next = new Node( 5 ); list.head.next.next.next.next.next = new Node( 6 ); list.head.next.next.next.next.next.next = new Node( 7 ); System.out.println( "Linked list before calling pairwiseSwap() " ); list.printList(head); head = list.pairWiseSwap(head); System.out.println( "" ); System.out.println( "Linked list after calling pairwiseSwap() " ); list.printList(head); System.out.println( "" ); } } |
Output:
Linked list before calling pairWiseSwap() 1 2 3 4 5 6 7 Linked list after calling pairWiseSwap() 2 1 4 3 6 5 7
Time Complexity: O(n)
Auxiliary Space: O(n)
Please refer complete article on Pairwise swap elements of a given linked list by changing links for more details!