题解 | #链表内指定区间反转#

/**
 * struct ListNode {
 *  int val;
 *  struct ListNode *next;
 *  ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
class Solution {
  public:
    /**
     * 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
     */
    ListNode* reverseBetween(ListNode* head, int m, int n) {
        if (m == n) return head;
        ListNode* virhead = new ListNode(-1);
        virhead->next = head;

        ListNode* pre = virhead;
        for (int i = 1; i < m; i++) pre = pre->next;
        ListNode* curr = pre->next, *post = curr->next;
        for (int i = 0; i < n - m; i++) {
            ListNode* tmp = post->next;
            post->next = curr;
            curr = post;
            post = tmp;
        }
        pre->next->next = post;
        pre->next = curr;
        ListNode* ret = virhead->next;
        delete virhead;
        return ret;
    }
};