leetcode-----25. K 个一组翻转链表

• 链接：https://leetcode-cn.com/problems/reverse-nodes-in-k-group/

代码

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseKGroup(ListNode* head, int k) {
        auto dummy = new ListNode(-1);
        dummy->next = head;
        for (auto p = dummy;;) {
            auto q = p;
            for (int i = 0; i <k && q; ++i) q = q->next;
            if (!q) break;
            auto a = p->next, b = a->next;
            for (int i = 0; i < k - 1; ++i) {
                auto c = b->next;
                b->next = a;
                a = b, b = c;
            }
            auto c = p->next;
            p->next = a, c->next = b;
            p = c;
        }
        return dummy->next;
    }
};