<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:
    
    stack<int> CollectTheDataInStack(ListNode* head)
    {
        ListNode* temp = head;
        stack<int> st;
        while(temp != nullptr)
        {
            st.push(temp->val);
            temp = temp->next;
        }

        return st;
    }

    void insert(ListNode* head, int val)
    {
        ListNode* newNode = new ListNode(val);

        if (head->val == 0)// empty
        {
            head->val = val;
        }
        else if (head->next == nullptr)
        {
            head->next = newNode;
        }
        else
        {
            ListNode* temp = head;

            while (temp->next != nullptr)
                temp = temp->next;

            temp->next = newNode;
        }
    }

    void reorderList(ListNode*& head) {
        
        ListNode* temp = head;
        ListNode* NewList = new ListNode();

        stack<int> st = CollectTheDataInStack(head);
        int size = st.size();
        int idx = 1;

        while(size != 0)
        {
            if(idx % 2 == 1)
            {
                insert(NewList, temp->val);
                temp = temp->next;
            }
            else
            {
                insert(NewList, st.top());
                st.pop();
            }

            idx++;
            size--;
        }

        temp = head;
        while(temp != nullptr)
        {
            ListNode* temp2 = NewList;

            temp->val = NewList->val;

            temp = temp->next;

            NewList = NewList->next;
            delete temp2;
        }
    }
};
25500