leecode-21. 合并两个有序链表

  • 将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。 
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示例：

输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4

解法一：

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
# author：sarizzm time:2020/12/24 0024

# Definition for singly-linked list.
class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next
class Solution:
    def mergeTwoLists(self, l1, l2):

        if not l1:return l2
        if not l2:return l1
        p1 = l3 = ListNode()
        while (l1 and l2):
            if l1.val < l2.val:
                p1.next = l1
                l1 = l1.next
                p1 = p1.next
            else:
                p1.next = l2
                l2 = l2.next
                p1 = p1.next
        if l1 == None:
            p1.next = l2
            return l3.next
        else:
            p1.next = l1
            return l3.next

def generateNode(nx):
    node = ListNode()
    p1 = node

    for i in nx:
        p1.next = ListNode(i)
        p1 = p1.next
    return node.next
n1 = [1,3,5,7,10]
n2 = [2,4,6,8,9]
node1 = generateNode(n1)
node2 = generateNode(n2)
# while(node1):
#     print(node1.val)
#     node1 = node1.next

node3 = Solution().mergeTwoLists(node1,node2)
while(node3):
    print(node3.val)
    node3 = node3.next

解法二

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class Solution:
    def mergeTwoLists(self, l1, l2):
        if l1 is None:
            return l2
        elif l2 is None:
            return l1
        elif l1.val < l2.val:
            l1.next = self.mergeTwoLists(l1.next, l2)
            return l1
        else:
            l2.next = self.mergeTwoLists(l1, l2.next)
            return l2

#作者：LeetCode-Solution
#链接：https://leetcode-cn.com/problems/merge-two-sorted-lists/solution/he-bing-liang-ge-you-xu-lian-biao-by-leetcode-solu/


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class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) {
            return l2;
        } else if (l2 == null) {
            return l1;
        } else if (l1.val < l2.val) {
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        } else {
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        }

    }
}

//作者：LeetCode-Solution
//链接：https://leetcode-cn.com/problems/merge-two-sorted-lists/solution/he-bing-liang-ge-you-xu-lian-biao-by-leetcode-solu/