【leetcode】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.

 /**
  * 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) {
         int d=n-m;
         if(head==NULL||head->next==NULL||d<=)
             return head;

         ListNode* p=head,*bfp=p;
         ListNode* q=head;
         for(int i=;i<m-;i++){
             bfp=p;
             p=p->next;
         }
         ListNode* revhead=p;
         ListNode* bf=p,*bh=NULL;
         p=p->next;
         d--;
         while(p->next!=NULL&&d!=){
             d--;
             bh=p->next;
             p->next=bf;
             bf=p;
             p=bh;

         }
         bh=p->next;
         p->next=bf;
         bfp->next=p;
         revhead->next=bh;
         if(m!=)
             return head;
         else return p;
     }
 };