【LeetCode】C# 92、Reverse Linked List II

Reverse a linked list from position m to n. Do it in-place and in one-pass.

For example:

Given 1->2->3->4->5->NULL, m = 2 and n = 4,

return 1->4->3->2->5->NULL.

Note:

Given m, n satisfy the following condition:

1 ≤ m ≤ n ≤ length of list.

给定链表和两个数值，将链表中对应两个位置的那段链表反转。

思路：建立4个指针。dummy指向head，pre指向第一个要翻转的节点，然后start指向下一个操作要翻转到前面的节点。then指向start.next，用来辅助翻转。

/**
* Definition for singly-linked list.
* public class ListNode {
*     public int val;
*     public ListNode next;
*     public ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode ReverseBetween(ListNode head, int m, int n) {
if(head == null) return null;
ListNode dummy = new ListNode(0);
dummy.next = head;
ListNode pre = dummy;
for(int i = 0; i<m-1; i++) pre = pre.next;

ListNode start = pre.next;
ListNode then = start.next;

for(int i=0; i<n-m; i++)
{
start.next = then.next;
then.next = pre.next;
pre.next = then;
then = start.next;
}
return dummy.next;
}
}