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21.py
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21.py
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# Name: Merge Two Sorted Lists
# Link: https://leetcode.com/problems/merge-two-sorted-lists/
# Method: Zipper merge, with lefover head check
# Time: O(n)
# Space: O(1)
# Difficulty: Easy
# 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:
merged_list_head = ListNode()
head_now = merged_list_head
l1_head = l1
l2_head = l2
while l1_head is not None and l2_head is not None:
if l1_head.val < l2_head.val:
head_now.next = l1_head
l1_head = l1_head.next
else:
head_now.next = l2_head
l2_head = l2_head.next
head_now = head_now.next
head_now.next = None
for leftover_head in (l1_head, l2_head):
while leftover_head is not None:
head_now.next = leftover_head
head_now = head_now.next
leftover_head = leftover_head.next
merged_list_head = merged_list_head.next # Remove dummy start node
return merged_list_head