/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* reverseBetween(struct ListNode* head, int m, int n) {
    struct ListNode *pNode = head, *tmp_1, *tmp_2, *tmp_head = NULL, *tmp_tail;
    int count = 0;
    
    if(1 != m){
        while(NULL != pNode){
            count++;
            if(m - 1 == count){
                tmp_tail = tmp_1 = pNode->next;
                pNode->next = NULL;
                while(n > count){
                    tmp_2 = tmp_1->next;
                    tmp_1->next = pNode->next;
                    pNode->next = tmp_1;
                    tmp_1 = tmp_2;
                    count++;
                }
                tmp_tail->next = tmp_1;
                break;
            }
            pNode = pNode->next;
        }
    }
    else{
        tmp_tail = head;
        while(n > count){
            tmp_2 = head->next;
            head->next = tmp_head;
            tmp_head = head;
            head = tmp_2;
            count++;
        }
        tmp_tail->next = head;
        head = tmp_head;
    }
    return head;
}