[Leetcode]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.
比较基础的链表题，精髓在于使用dummy节点来方便的维护链表头。

public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(0);
        ListNode temp = dummy;
        while(l1 != null && l2 != null) {
            if(l1.val < l2.val) {
                temp.next = l1;
                temp = temp.next;
                l1 = l1.next;
            }
            else {
                temp.next = l2;
                temp = temp.next;
                l2 = l2.next;
            }
        }
        temp.next = l1 == null ? l2 : l1;
        return dummy.next;
 }
}