92.md

Reverse Linked List II

Description

link

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Solution

See Code

注意代码最后两行，拼接的时候，先指定next.next，然后指定next，可以使得不论next接了多少个node，都可以在最后那个node后接上next.next

理解错误，因为pre.next本来就是连在第二部分的最后一段，所以可以直接使用next next的方法来接上第三段

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Code

O(n)

class Solution:
    def reverseBetween(self, head, m, n):
        """
        :type head: ListNode
        :type m: int
        :type n: int
        :rtype: ListNode
        """
        dummy = pre = ListNode(0)
        dummy.next = head
        for _ in range(m-1):
            pre = pre.next
        cur = pre.next
        # reverse the defined part
        node = None
        for _ in range(n-m+1):
            nxt = cur.next
            cur.next = node
            node = cur
            cur= nxt
        # connect three parts
        pre.next.next = cur
        pre.next = node
        return dummy.next