將兩個升序鏈表合并為一個新的 升序 鏈表并返回。新鏈表是通過拼接給定的兩個鏈表的所有節(jié)點組成的涨颜。
示例 1：
輸入：l1 = [1,2,4], l2 = [1,3,4]
輸出：[1,1,2,3,4,4]
示例 2：
輸入：l1 = [], l2 = []
輸出：[]
示例 3：
輸入：l1 = [], l2 = [0]
輸出：[0]
提示：
兩個鏈表的節(jié)點數(shù)目范圍是 [0, 50]
-100 <= Node.val <= 100
l1 和 l2 均按 非遞減順序 排列
方法一：
# 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: ListNode, l2: ListNode) -> ListNode:
dummy = ListNode()
curr = dummy
while l1 and l2:
if l1.val < l2.val:
curr.next = l1
l1 = l1.next
else:
curr.next = l2
l2 = l2.next
curr = curr.next
if l1:
curr.next = l1
if l2:
curr.next = l2
return dummy.next
方法二：遞歸，待修正
class Solution:
def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
if l1 != None or l2 != None:
if l1:
return l1
else:
return l2
# return l1 if l1 else l2
if l1.val < l2.val:
l1.next = mergeTwoLists(l1.next, l2)
return l1
else:
l2.next = mergeTwoLists(l1, l2.next)
return l2
