MergeTwoLists.java

package LeetcodePractice;
import java.util.List;

public class MergeTwoLists {
    static class ListNode {
        int val;
        ListNode next;
        ListNode() {}
        ListNode(int val) { this.val = val; }
        ListNode(int val, ListNode next) { this.val = val; this.next = next; }
    }

    public static ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        ListNode dummy = new ListNode(-1);
        ListNode current = dummy;

        while (list1 != null && list2 != null) {
            if (list1.val <= list2.val) {
                current.next = list1;
                list1 = list1.next;
            } else {
                current.next = list2;
                list2 = list2.next;
            }
            current = current.next;
        }

     
        if (list1 != null) {
            current.next = list1;
        } else if (list2 != null) {
            current.next = list2;
        }

        return dummy.next;
    }

    
    public void printList(ListNode head) {
        while (head != null) {
            System.out.print(head.val + " -> ");
            head = head.next;
        }
        System.out.println("null");
    }

    public static void main(String[] args) {

        
        ListNode list1 = new ListNode(1, new ListNode(2, new ListNode(4)));
        ListNode list2 = new ListNode(1, new ListNode(3, new ListNode(4)));

        ListNode merged = mergeTwoLists(list1, list2);
        System.out.print("Merged List: ");
        while (merged != null) {
            System.out.print(merged.val);
            if (merged.next != null) {
                System.out.print(" -> ");
            }
            merged = merged.next;
        }
        System.out.println(); 
    }
}