[LeetCode]21、Merge Two Sorted Lists

题目描述：

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.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

思路：

　　将两个排好序的链表合并，依次比较两个链表的数字，存入第三个链表中

public class Solution21 {
    public ListNode mergeTwoLists(ListNode l1,ListNode l2){
        ListNode l3 = new ListNode(0);
        ListNode dummy = l3;
        while(l1 != null && l2 != null){
            if(l1.val< l2.val){
                l3.next =l1;
                l1 = l1.next;
            }else {
                l3.next = l2;
                l2 = l2.next;
            }
            l3 = l3.next;
        }
        l3.next = (l1 == null)?l2:l1;
        return dummy.next;
    }
    public static void main(String[] args){
        // TODO Auto-generated method stub
        Solution21 solution21 = new Solution21();
        ListNode l1 = new ListNode(1);
        ListNode l2 = new ListNode(2);
        
        System.out.println(solution21.mergeTwoLists(l1, l2));
    }

}