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[LeetCode] 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->NULLm = 2 and n = 4,

return 1->4->3->2->5->NULL.

Note:
Given mn satisfy the following condition:
1 ≤ m ≤ n ≤ length of list.

 

 1 /** 2  * Definition for singly-linked list. 3  * struct ListNode { 4  *     int val; 5  *     ListNode *next; 6  *     ListNode(int x) : val(x), next(NULL) {} 7  * }; 8  */ 9 class Solution {10 public:11     ListNode *reverseBetween(ListNode *head, int m, int n) {12         if (head == NULL || m > n) return NULL;13         ListNode* pmprev = NULL;// 始终指向第m个节点的前缀14         ListNode* pn = NULL; //指向逆置后的第n个节点15         ListNode* pm = NULL; //指向第m个节点16         ListNode *pter = NULL; //操作节点17         ListNode *pter_next = NULL; //指向操作节点的下一个节点18         pter = head;19         20         for (int i = 1; i < m; ++i) {21             pmprev = pter;22             pter = pter->next;23         }24         25         pn = pm = pter;26         for (int i = m; i <= n; ++i) {27             pter_next = pter->next;28             pter->next = pn;29             pn = pter;30             pter = pter_next;31         }32         33         if (pmprev == NULL) { //如果头结点也在逆置范围中34             head = pn;35         } else {36             pmprev->next = pn;37         }38         39         pm->next = pter_next;40         41         return head;42     }43 };

 

[LeetCode] Reverse Linked List II