Reverse Linked List II

未完成，还可以找到更好的解

/**
 * 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 *before = new ListNode(0);
        before->next = head;
        for (int i = 1; i < m; ++i)
            before = before->next;
        
        ListNode *cur = before->next;
        ListNode *cur_fol = cur->next;
        ListNode *behind = cur_fol;
        
        for (int i = m; i < n; ++i)
            behind = behind->next;
        
        int num = n - m + 1;
        while (num--) {
            cur->next = behind;
            behind = cur;
            cur = cur_fol;
            if (cur_fol)
                cur_fol = cur_fol->next;
        }
        
        if (m == 1)
            head = behind;
        else
            before->next = behind;
        
        return head;
            
    }
};