合并两个排序的链表

题目描述
输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则。
递归：注意链表为空的情况；

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    # 返回合并后列表
    def Merge(self, pHead1, pHead2):
        # write code here
        if pHead1==None:
            return pHead2
        if pHead2==None:
            return pHead1
        if pHead1.val<pHead2.val:
            res=pHead1
            res.next=self.Merge(pHead1.next,pHead2)
        else:
            res=pHead2
            res.next=self.Merge(pHead1,pHead2.next)
        return res

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

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode Merge(ListNode list1,ListNode list2) {
        if(list1==null) return list2;
        if(list2==null) return list1;
        ListNode res=null;//先初始化一个res
        if(list1.val<list2.val){
            res=list1;
            res.next=Merge(list1.next,list2);
        }
        else{
            res=list2;
            res.next=Merge(list1,list2.next);
        }
        return res;
    }
}