LeetCode 0025 - Reverse Nodes in k-Group

Reck Zhang

发布于 2021-08-11 10:19:28

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发布于 2021-08-11 10:19:28

文章被收录于专栏：Reck Zhang

Reverse Nodes in k-Group

Desicription

Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.

k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is.

You may not alter the values in the nodes, only nodes itself may be changed.

Only constant memory is allowed.

For example,

Given this linked list: 1->2->3->4->5

For k = 2, you should return: 2->1->4->3->5

For k = 3, you should return: 3->2->1->4->5

Solution

/**
 * 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) {
        ListNode* travel = head;
        ListNode* res = new ListNode(0);
        ListNode* res_travel = res;
        vector<int>tmp;
        while(travel){
            tmp.push_back(travel->val);
            if(tmp.size() == k){
                for(int i = tmp.size()-1; i >= 0; i--){
                    res_travel->next = new ListNode(tmp[i]);
                    res_travel = res_travel->next;
                }
                tmp.clear();
            }
            travel = travel->next;
        }
        if(!tmp.empty())
            for(int i = 0; i < tmp.size(); i++)
                res_travel->next = new ListNode(tmp[i]), res_travel = res_travel->next;
        return res->next;
    }
};

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