Reverse Linked List II

Problem: Reverse Linked List II

I use a dummy solution to find the two nodes whether targeted linked list is wrapped and cut it out for reversion. A better solution is to reverse the linked list as soon as we find head of target and stop reversing at tail of target.

Code in Python:

# 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):
        """
        :type head: ListNode
        :type m: int
        :type n: int
        :rtype: ListNode
        """
        dummy = ListNode(0)
        dummy.next = head
        prev, node = dummy, head
        i = 0
        l, r, lp = None, None, None
        while i != n and node:
            if i == m-1: prev.next, l, lp = None, node, prev
            prev, node = node, node.next
            i += 1
        prev.next, r = None, node

        p = None
        node = l
        while node:
            tmp = node.next
            node.next, p, node = p, node, tmp
        lp.next, l.next = p, r
        return dummy.next