题解 | #链表内指定区间反转#

/**
 * struct ListNode {
 *  int val;
 *  struct ListNode *next;
 * };
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 *
 * @param head ListNode类
 * @param m int整型
 * @param n int整型
 * @return ListNode类
 */
struct ListNode* reverseBetween(struct ListNode* head, int m, int n ) {
    if (head == NULL || head->next == NULL)
        return head;

    int change_len = n - m + 1;
    struct ListNode *pre_head = NULL;
    struct ListNode *result = head;
    while (head && --m)
    {
        pre_head = head;
        head = head->next;
    }
    struct ListNode *modify_list_tail = head;
    struct ListNode *new_head = NULL;
    while (head && change_len)
    {
        struct ListNode *next = head->next;
        head->next = new_head;
        new_head = head;
        head = next;
        change_len--;
    }
    modify_list_tail->next = head;
    if (pre_head)
        pre_head->next = new_head;
    else
        result = new_head;
    return result;
}