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.

先反转m到n之间的list再头尾衔接一下

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *reverseBetween(ListNode *head, int m, int n) {
ListNode dummy(-1);
dummy.next=head;
ListNode* pm=&dummy;
for(int i=0;i<m-1;i++)
pm=pm->next;
ListNode* start=pm;
pm=pm->next;
ListNode* begin=pm;
ListNode *next,*cur=pm->next;
for(int i=n-m;i>0;i--)
{
next=cur->next;
cur->next=pm;
pm=cur;
cur=next;
}
start->next=pm;
begin->next=cur;
return dummy.next;
}
};