03_MergeSortedLists.java

// Problem: Merge Two Sorted Linked Lists
// Author: Ataul (codeByunique)

class ListNode {
    int val;
    ListNode next;
    ListNode(int val) {
        this.val = val;
    }
}

class MergeSortedLists {
    public static void main(String[] args) {
        // List 1: 1 -> 3 -> 5
        ListNode l1 = new ListNode(1);
        l1.next = new ListNode(3);
        l1.next.next = new ListNode(5);

        // List 2: 2 -> 4 -> 6
        ListNode l2 = new ListNode(2);
        l2.next = new ListNode(4);
        l2.next.next = new ListNode(6);

        ListNode merged = mergeTwoLists(l1, l2);

        System.out.print("Merged List: ");
        while (merged != null) {
            System.out.print(merged.val + " ");
            merged = merged.next;
        }
    }

    public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(-1);
        ListNode tail = dummy;

        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                tail.next = l1;
                l1 = l1.next;
            } else {
                tail.next = l2;
                l2 = l2.next;
            }
            tail = tail.next;
        }

        // Attach the remaining part
        tail.next = (l1 != null) ? l1 : l2;

        return dummy.next;
    }
}