92. Reverse Linked List II

2019-06-25

92. Reverse Linked List II

Reverse a linked list from position _m_ to _n_. Do it in one-pass.

Note: 1 ≤ _m_ ≤ _n_ ≤ length of list.

Example:

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Input: 1->2->3->4->5->NULL, m = 2, n = 4
Output: 1->4->3->2->5->NULL

Code:

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# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def reverseBetween(self, head, m, n):
        dummy = ListNode(0)
        dummy.next = head

        cur, prev = head, dummy
        for _ in range(m - 1):
            cur = cur.next
            prev = prev.next

        for _ in range(n - m):
            temp = cur.next
            cur.next = temp.next
            temp.next = prev.next
            prev.next = temp

        return dummy.next
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