題目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.

1

public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1 == null){
            return l2;
        }
        
        if(l2 == null){
            return l1;
        }
        
        ListNode newHead = new ListNode(-99);
        ListNode newTail = newHead;
        ListNode first = l1;
        ListNode second = l2;
        while(first != null && second != null){
            if(first.val > second.val){
                newTail.next = second;
                second = second.next;
            }else{
                newTail.next = first;
                first = first.next;
            }
            newTail = newTail.next;
        }
        
        if(first == null){
            newTail.next = second;
        }
        
        if(second == null){
            newTail.next = first;
        }
        return newHead.next;
    }
}