/**
 * 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:
    void reorderList(ListNode* head) {
        ListNode *tmp = head;
        vector<int> arr_num;
        while(tmp!=nullptr)
        {
            arr_num.push_back(tmp->val);
            tmp = tmp -> next;
        }
        int node_num = arr_num.size()/2;
        tmp = head;
        ListNode *tmp_next;
        while(node_num--)
        {
            ListNode *new_node = new ListNode(arr_num[arr_num.size()  - ( arr_num.size()/2 - node_num)]);
            // cout<<new_node->val<<endl;
            tmp_next = tmp->next;
            tmp->next = new_node;
            new_node->next = tmp_next;
            if(node_num == 0 && arr_num.size()%2 == 0) new_node->next = nullptr;
            else if(node_num == 0 && arr_num.size()%2 == 1) new_node->next->next = nullptr;
            else tmp = tmp->next->next;
        }
    }
};