LeetCode 92. Reverse Linked List II

/** * 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 dummy(0);        ListNode *pre = &dummy;        dummy.next = head;        for (int i = 1; i < m; ++i) {            pre = pre->next;        }        head = pre->next;        ListNode *cur = head->next;        for (int i = m; i < n; ++i) {            ListNode *temp = cur->next;            cur->next = pre->next;            pre->next = cur;            cur = temp;        }        head->next = cur;        return dummy.next;    }};

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.