LeetCode#25.K 个一组翻转链表

25. K 个一组翻转链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseKGroup(ListNode* head, int k) {
        if(!head || !head->next || k<=1) return head;
        ListNode * cur=head;
        vector<ListNode*> list;
        while(cur){
            list.push_back(cur);
            cur=cur->next;
        }
        if(list.size()<k) return head;
        ListNode *dhead=new ListNode(-1),*pre=dhead;
        for(int i=0;i<list.size()/k*k;i+=k){
            pre->next=list[i+k-1];
            for(int j=k-1;j>=1;--j){
                 list[j+i]->next=list[j+i-1];
            }
            pre=list[i];
        }
        if(list.size()%k!=0){
            pre->next=list[list.size()/k*k];
        }else{
            pre->next=nullptr;
        }
        return dhead->next;
    }
};