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72 lines
1.5 KiB
Python
72 lines
1.5 KiB
Python
"""
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92. Reverse Linked List II
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Difficulty: Medium
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https://leetcode.com/problems/reverse-linked-list-ii/
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──────────────────────────────────────────────────
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Given the head of a singly linked list and two integers left and
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right where left <= right, reverse the nodes of the list from position
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left to position right, and return the reversed list.
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Example 1:
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Input: head = [1,2,3,4,5], left = 2, right = 4
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Output: [1,4,3,2,5]
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Example 2:
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Input: head = [5], left = 1, right = 1
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Output: [5]
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Constraints:
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• The number of nodes in the list is n.
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• 1 <= n <= 500
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• -500 <= Node.val <= 500
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• 1 <= left <= right <= n
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Follow up: Could you do it in one pass?
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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 reverseBetween(
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self, head: ListNode | None, left: int, right: int
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) -> ListNode | None:
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cur, prev = head, None
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while left > 1:
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prev = cur
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cur = cur.next
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left, right = left - 1, right - 1
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tail, con = cur, prev
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while right:
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third = cur.next
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cur.next = prev
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prev = cur
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cur = third
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right -= 1
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if con:
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con.next = prev
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else:
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head = prev
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tail.next = cur
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return head
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