剑指面试题25-合并两个排序的链表

题目：输入两个递增排序的链表，合并这两个链表并使新链表中的节点仍然是递增排序的。例如，输入图3.11中的链表1和链表2，则合并之后的升序链表如链表3所示。

此思路类似归并排序

# -*- 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
        elif pHead2 == None:
            return pHead1
        pMergedHead = None
        if pHead1.val < pHead2.val:
            pMergedHead = pHead1
            pMergedHead.next = self.Merge(pHead1.next,pHead2)
        else:
            pMergedHead = pHead2
            pMergedHead.next = self.Merge(pHead1, pHead2.next)
        return pMergedHead