reverse linked list2

class Solution {
public:
    ListNode *reverseBetween(ListNode *head, int m, int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        ListNode * root = new ListNode(0);
        root->next = head;
        ListNode* ptr = root;
        for(int i=1;i<m;i++)
            ptr = ptr->next;
            
        ListNode * p = ptr->next;
        ListNode * q;
        for(int i=1;i<=n-m;i++)
        {
            q = ptr->next;
            ptr->next = p->next;
            p->next = ptr->next->next;
            ptr->next->next = q;   
            
        }
        return root->next;
        
        
        
    }
};