[leetcode] Reverse Linked List II

From : https://leetcode.com/problems/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.

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Linked List

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(E) Reverse Linked List

Solution :

/**
* 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) {
if(m == n) return head;
ListNode *tHead = new ListNode(0), *pre, *rtail, *p, *t;
tHead->next = head;
pre = tHead;
for(int i=1; i<m; i++) {
pre = pre->next;
}
rtail = pre->next;
p = rtail->next;
for(int k=n-m; k>0; k--) {
rtail->next = p->next;
t = pre->next;
pre->next = p;
p->next = t;
p = rtail->next;
}
p = tHead->next;
delete tHead;
return p;
}
};