Java: Swap every two adjacent nodes of a given linked list

Last update on May 13 2025 13:00:28 (UTC/GMT +8 hours)

Swap Adjacent Nodes in List

Write a Java program to swap two adjacent nodes in a linked list.

Visual Presentation:

Sample Solution:

Java Code:

// Importing necessary Java utilities
import java.util.*;

// Main class Solution
public class Solution {
    // Main method
    public static void main(String[] args) {
        // Creating a linked list
        ListNode l = new ListNode(10);
        l.next = new ListNode(20);
        l.next.next = new ListNode(30);
        l.next.next.next = new ListNode(40);
        l.next.next.next.next = new ListNode(50);
        
        // Printing original linked list
        System.out.println("\nOriginal Linked list:");
        printList(l);
        
        // Swapping pairs of nodes in the linked list
        ListNode p = swap_Pairs(l);
        
        // Printing linked list after swapping pairs
        System.out.println("\n\nAfter swapping, Linked list becomes:");
        printList(p);
    }
    
    // Method to swap pairs of nodes in a linked list
    public static ListNode swap_Pairs(ListNode head) {
        ListNode temp = new ListNode(0); // Creating a temporary node
        temp.next = head; // Setting temp node's next to the head of the original linked list
        head = temp; // Assigning head to temp
        
        // Swapping pairs using iterative approach
        while (head.next != null && head.next.next != null) {
            ListNode a = head.next;
            ListNode b = head.next.next;
            head.next = b;
            a.next = b.next;
            b.next = a;
            head = a;
        }
        return temp.next; // Returning the modified linked list
    }

    // Method to print the linked list
    static void printList(ListNode p) {
        while (p != null) {
            System.out.print(p.val); // Printing node value
            if (p.next != null) {
                System.out.print("->"); // Adding "->" if more nodes are present
            }
            p = p.next; // Moving to the next node
        }
    }
}

// Definition of ListNode class
class ListNode {
    int val;
    ListNode next;

    ListNode(int x) {
        val = x;
    }
} 

Sample Output:

Original Linked list:
10->20->30->40->50

After swiping Linked list becomes:
20->10->40->30->50

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to reverse a linked list in pairs.
• Write a Java program to swap two nodes at specified indices in a singly linked list.
• Write a Java program to swap adjacent nodes in a linked list without swapping the actual node data.
• Write a Java program to swap every third node with its preceding node in a linked list.

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• Java Basic Part-II Programming Exercises Home ↩
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