合并两个排序的链表

# -*- 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 is None:  #首先考虑极端的特殊情况
            return pHead2
        if pHead2 is None:
            return pHead1
        pMergeHead = None
        if pHead1.val<pHead2.val:
            pMergeHead = pHead1
            pMergeHead.next = self.Merge(pHead1.next,pHead2) #这里递归的时候方法的调用依然要用类实例.方法，而类中的self就是指类实例
        else:
            pMergeHead = pHead2
            pMergeHead.next = self.Merge(pHead2.next,pHead1) 
        return pMergeHead   #递归的输出是两个链表排序合并后的列表的指针（就是这个链表）