leetcode 25. K 个一组翻转链表

/**
 * 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) {
        if(head == nullptr)
        {
            return nullptr;
        }
        vector<int> vec;
        vector<int> v;
        vector<int> temp;
        while(head)
        {
            vec.push_back(head->val);
            head = head->next;
        }
        int len = vec.size();
        int length = len / k * k;
        for(int i = 0; i < length;)
        {
            temp.assign(&vec[i], &vec[i + k]);
            reverse(temp.begin(), temp.end());
            for(int i = 0; i < temp.size(); i++)
            {
                v.push_back(temp[i]);
            }
            temp.clear();
            i += k;
        }
        for(int i = length; i < len; i++)
        {
            v.push_back(vec[i]);
        }
        ListNode* res = new ListNode(0);
        ListNode* dummynode = res;
        for(int i = 0; i < v.size(); i++)
        {
            dummynode->val = v[i];
            if(i == v.size() - 1)
            {
                break;
            }
            dummynode->next = new ListNode(0);
            dummynode = dummynode->next;
        }
        return res;
    }
};