合并有序链表

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param l1 ListNode类 
     * @param l2 ListNode类 
     * @return ListNode类
     */
    public ListNode mergeTwoLists (ListNode l1, ListNode l2) {
        // write code here
        ListNode node = null;
        ListNode head = null;
        if(l1==null){
            return l2;
        }
        if(l2==null){
            return l1;
        }
        if(l1.val<l2.val){
            node = l1;
            l1=l1.next;
        }else{
            node = l2;
            l2=l2.next;
        }
        head = node;
        while(l1!=null&&l2!=null){
            if(l1.val < l2.val){
                node.next = l1;
                l1=l1.next;
            }else{
                node.next = l2;
                l2=l2.next;
            }
            node = node.next;
        }
        if(l1!=null){
            node.next = l1;
        }else{
            node.next = l2;
        }

        return head;
    }
}