两个链表归并

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。 

# -*- 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
        
        temp_head = None         # 辅助链表的当前位置
        
        
        if pHead1 == None:
            return pHead2
        if pHead2 == None:
            return pHead1
        
        if pHead1.val<=pHead2.val:
            temp_head = pHead1
            pHead1 = pHead1.next
        else:
            temp_head = pHead2
            pHead2 = pHead2.next
        
        head = temp_head        # 辅助链表的头位置
        
        while pHead1!=None and pHead2!=None:
            if (pHead1.val<=pHead2.val):
                temp_head.next = pHead1
                pHead1 = pHead1.next
                temp_head = temp_head.next
            else:
                temp_head.next = pHead2
                pHead2 = pHead2.next
                temp_head = temp_head.next
        
        if pHead1==None:
            temp_head.next = pHead2
        if pHead2 == None:
            temp_head.next = pHead1
            
        return head            # 返回辅助链表的头位置