21. Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        // if (l1 == null) {
        //     return l2;
        // }
        // if (l2 == null) {
        //     return l1;
        // }
        ListNode dummy = new ListNode(0);
        ListNode head = dummy;
        while (l1 != null && l2 != null) {
            if (l1.val > l2.val) {
                head.next = l2;
                l2 = l2.next;
            } else {
                head.next = l1;
                l1 = l1.next;
            }
            head = head.next;
            
        }
        if (l1 == null) {
            head.next = l2;
        }
        if (l2 == null) {
            head.next = l1;
        }
        return dummy.next;
    }
}
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