Reorder List [LeetCode]

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: make sure the last element points to NULL in the new list;

    void reorderList(ListNode *head) {
        vector<ListNode * > nodes;
        ListNode * current = head;
        while(current != NULL) {
            nodes.push_back(current);
            current = current->next;
        }
        for(int i = 0; i < nodes.size() / 2; i ++){
            int next = nodes.size() - 1 - i;
            if(i < next){
                ListNode * tmp = nodes[i]->next;
                nodes[i]->next = nodes[next];
                nodes[next]->next = tmp;
            }
        }
        if(nodes.size() > 0)
            nodes[nodes.size() / 2]->next = NULL;
    }

    void reorderList(ListNode *head) {
        vector<ListNode * > nodes;
        ListNode * current = head;
        while(current != NULL) {
            nodes.push_back(current);
            current = current->next;
        }
        for(int i = 0; i < nodes.size() / 2; i ++){
            if(i < nodes.size() - 1 - i){
                nodes[i]->next = nodes[nodes.size() - 1 - i];
                if(i + 1 < nodes.size() - 1 - i)
                    nodes[nodes.size() - 1 - i]->next = nodes[i + 1];
                else
                    nodes[nodes.size() - 1 - i]->next = NULL;
            }
        }
        if(nodes.size() % 2 == 1)
            nodes[nodes.size() / 2]->next = NULL;
    }