Leetcode139: Reverse Linked List II

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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) {if (head == NULL)return NULL;ListNode *q = NULL;ListNode *p = head;for(int i = 0; i < m - 1; i++){q = p;p = p->next;}ListNode *end = p;ListNode *pPre = p;p = p->next;for(int i = m + 1; i <= n; i++){ListNode *pNext = p->next;p->next = pPre;pPre = p;p = pNext;}end->next = p;if (q)q->next = pPre;elsehead = pPre;return head;}
};

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