<p>You are given the head of a singly linked-list. The list can be represented as:</p>

<pre>
L<sub>0</sub> &rarr; L<sub>1</sub> &rarr; &hellip; &rarr; L<sub>n - 1</sub> &rarr; L<sub>n</sub>
</pre>

<p><em>Reorder the list to be on the following form:</em></p>

<pre>
L<sub>0</sub> &rarr; L<sub>n</sub> &rarr; L<sub>1</sub> &rarr; L<sub>n - 1</sub> &rarr; L<sub>2</sub> &rarr; L<sub>n - 2</sub> &rarr; &hellip;
</pre>

<p>You may not modify the values in the list&#39;s nodes. Only nodes themselves may be changed.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/03/04/reorder1linked-list.jpg" style="width: 422px; height: 222px;" />
<pre>
<strong>Input:</strong> head = [1,2,3,4]
<strong>Output:</strong> [1,4,2,3]
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/03/09/reorder2-linked-list.jpg" style="width: 542px; height: 222px;" />
<pre>
<strong>Input:</strong> head = [1,2,3,4,5]
<strong>Output:</strong> [1,5,2,4,3]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the list is in the range <code>[1, 5 * 10<sup>4</sup>]</code>.</li>
	<li><code>1 &lt;= Node.val &lt;= 1000</code></li>
</ul>

/**
 * 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) {
        ios_base::sync_with_stdio(false);
        cin.tie(nullptr);
        cout.tie(nullptr);

        deque<int> vals;
        ListNode *curr = head;
        while (curr != nullptr) {
            vals.push_back(curr->val);
            curr = curr->next;
        }

        curr = head;
        while (!vals.empty()) {
            curr->val = vals.front();
            vals.pop_front();
            curr = curr->next;
            if (!vals.empty()) {
                curr->val = vals.back();
                vals.pop_back();
                curr = curr->next;
            }
        }
    }
};
23400