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.
找到第m-1位置保存,将m到n位置依次next指针指向前一个元素,将第m位置元素指向n+1元素位置,m-1位置元素指向n位置元素,注意处理改变head时的情况,
我这里在头节点前加一元素好处理
/** * 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 *p=new ListNode(0); ListNode *q,*r,*link,*nh; p->next=head; nh=p; int count=0; while(p){ q=p->next; if(count==m-1)link=r=p; else if(count>=m&&count<=n){ p->next=r; r=p; } if(count==n){ link->next->next=q; link->next=p; } p=q; count++; } return nh->next; } };