LeetCode：92. 反转链表 II

1、题目描述

反转从位置 m 到 n 的链表。请使用一趟扫描完成反转。

说明:
1 ≤ m ≤ n ≤ 链表长度。

示例:

输入: 1->2->3->4->5->NULL, m = 2, n = 4
输出: 1->4->3->2->5->NULL

2、题解

2.1、解法一

class Solution:
    def reverseBetween(self, head, m, n):
        """
        :type head: ListNode
        :type m: int
        :type n: int
        :rtype: ListNode
        """
        # 反转
        count = 0
        node = head
        stack = []
        left = head
        right = None

        ret = []
        while node:
            count += 1
            if count <m:
                left = node
                ret.append(node.val)
            elif count >= m and count <=n:
                stack.append(node)
            elif count >n:
                right = node
                while len(stack):
                    tmp = stack.pop()
                    ret.append(tmp.val)
                    left.next = tmp
                    left = tmp
                left.next = right
                ret.append(right.val)

            node = node.next
        else:
            while len(stack):
                ret.append(stack.pop().val)
        return ret