[leetcode] Reverse Linked List II

题目：（LinkedList）

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.

 

题解：

/**
 * 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) {
        ListNode fakeHead = new ListNode(0);
        fakeHead.next = head ;
        
        if(head==null||head.next==null)
           return fakeHead.next;
           
        ListNode prev = fakeHead;
        ListNode curr = null;
        ListNode last = null;
        
        for(int i=0; i<n; i++)
        {
            if(i<m-1)
            {
                prev=prev.next;
            }
            else if(i==m-1)
            {
                last=prev.next;
                curr=last.next;
            }
            else
            {
                last.next=curr.next;
                curr.next=prev.next;
                prev.next=curr;
                curr=last.next;
            }
        }
 
        return fakeHead.next;
    }
}