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58 lines
1.1 KiB
Python
58 lines
1.1 KiB
Python
"""
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206. Reverse Linked List
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Difficulty: Easy
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https://leetcode.com/problems/reverse-linked-list/
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──────────────────────────────────────────────────
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Given the head of a singly linked list, reverse the list, and return
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the reversed list.
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Example 1:
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Input: head = [1,2,3,4,5]
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Output: [5,4,3,2,1]
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Example 2:
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Input: head = [1,2]
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Output: [2,1]
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Example 3:
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Input: head = []
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Output: []
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Constraints:
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• The number of nodes in the list is the range [0, 5000].
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• -5000 <= Node.val <= 5000
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Follow up: A linked list can be reversed either iteratively or
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recursively. Could you implement both?
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"""
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# Definition for singly-linked list.
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# class ListNode:
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# def __init__(self, val=0, next=None):
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# self.val = val
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# self.next = next
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class Solution:
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def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
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prev = None
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curr = head
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while curr:
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next_ = curr.next
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curr.next = prev
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prev = curr
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curr = next_
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return prev
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