python JZ25 合并两个排序的链表（剑指offer）_jz25合并两个排序的链表 python

题目要求:

思路:

思路1：递归
思路2：额外列表排序
思路3：常规遍历

代码如下:

思路1代码：

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param pHead1 ListNode类 
# @param pHead2 ListNode类 
# @return ListNode类
#
class Solution:
    def Merge(self , pHead1: ListNode, pHead2: ListNode) -> ListNode:
        if not pHead1: # pHead1为None时将pHead2整体返回
            return pHead2
        if not pHead2: # pHead2为None时将pHead1整体返回
            return pHead1
        if pHead1.val <= pHead2.val: # 值小的在前，后面指向第二小的值即可
            pHead1.next = self.Merge(pHead1.next,pHead2)
            return pHead1 # 将比较得到的小值返回
        else:
            pHead2.next = self.Merge(pHead1,pHead2.next)
            return pHead2
        # write code here
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思路2代码：

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param pHead1 ListNode类 
# @param pHead2 ListNode类 
# @return ListNode类
#
class Solution:
    def Merge(self , pHead1: ListNode, pHead2: ListNode) -> ListNode:
        if not pHead1:
            return pHead2
        if not pHead2:
            return pHead1
        node_list = []
        while pHead1:
            node_list.append(pHead1)
            pHead1 = pHead1.next
        while pHead2:
            node_list.append(pHead2)
            pHead2 = pHead2.next
        node_list.sort(key=lambda x:x.val)
        pHead = index = node_list[0]
        for item in node_list[1:]:
            index.next = item
            index = index.next
        return pHead
        # write code here
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思路3代码：

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param pHead1 ListNode类 
# @param pHead2 ListNode类 
# @return ListNode类
#
class Solution:
    def Merge(self , pHead1: ListNode, pHead2: ListNode) -> ListNode:
        if not pHead1:
            return pHead2
        if not pHead2:
            return pHead1
        pHead = index = ListNode(-1)
        while pHead1 and pHead2:
            if pHead1.val <= pHead2.val:
                index.next = pHead1
                pHead1 = pHead1.next
            else:
                index.next = pHead2
                pHead2 = pHead2.next
            index = index.next
        if pHead1:
            index.next = pHead1
        else:
            index.next = pHead2
        return pHead.next
        
        # write code here
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