LeetCode 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.

思路分析：这题和LeetCode Reverse Nodes in k-Group很类似，要求对给定起始和结束位置的部分链表进行反转操作，我直接使用的LeetCode Reverse Nodes in k-Group里面的反转链表的函数AC的，需要注意传入正确的BeginNode和EndNode，同时对m和n取值的corner case要考虑周全。

AC Code:

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { *         val = x; *         next = null; *     } * } */public class Solution {    public ListNode reverseBetween(ListNode head, int m, int n) {        if(head == null || head.next == null) return head;        int i = 1;        ListNode cur = head;        ListNode beginNode = null;        ListNode endNode = null;        while(cur != null){            if(i == m-1){                beginNode = cur;            }            if(i == n+1){                endNode = cur;            }            i++;            cur = cur.next;        }        if(n == 1 || m == i-1) return head;        if(m == 1){            ListNode fakeNode = new ListNode(-1);            fakeNode.next = head;            beginNode = fakeNode;        }        ListNode firstInReverse = reverseLinkedList(beginNode, endNode);        if(m == 1) return firstInReverse;        else return head;    }        //reverse nodes between beginNode and endNode(exclusively)//return the first node in the reversed partprivate static ListNode reverseLinkedList(ListNode beginNode, ListNode endNode) {// TODO Auto-generated method stubListNode head = beginNode.next;ListNode dummy = head;//use dummy to maintain the new headListNode pre = head;ListNode cur = pre.next;ListNode after = cur.next;while(cur != endNode){pre.next = after;cur.next = dummy;dummy = cur;cur = pre.next;if(cur == null) break;after = cur.next;}beginNode.next = dummy;//!after reverse, beginNode should also before the first Node, endNode should also before the last nodereturn dummy;}}