LeetCode (Reorder List)

Problem:

Given a singly linked list L: L0→L1→…→Ln-1→Ln,
reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…

You must do this in-place without altering the nodes' values.

For example,
Given {1,2,3,4}, reorder it to {1,4,2,3}.

Solution:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    void reorderList(ListNode* head) {
        if(!head || !head->next) return;
        vector<ListNode*> list;
        while(head){
            list.push_back(head);
            head = head->next;
        }
        int n = list.size();
        for(int i = 0; i < n / 2; i++){
            list[i]->next = list[n - i - 1];
            list[n - i - 1]->next = list[i + 1];
        }
        list[n / 2]->next = NULL;
    }
};