<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>

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(head==NULL || head->next == NULL) return head;
        ListNode* newHead = reverseList(head->next);
        head->next->next = head;
        head->next = NULL;
        return newHead;
    }
    void reorderList(ListNode* head) {
        ListNode* slow= head;
        ListNode* fast = head;
        while(fast->next!= NULL && fast->next->next!=NULL){
            slow = slow->next;
            fast=fast->next->next;
        }
        ListNode* b = reverseList(slow->next);
        ListNode* a= head;
        slow->next=NULL;
        // MEREGE ALTERNATIVELY
        ListNode* c= new ListNode(100);
        ListNode* tempc=c;
        ListNode* tempa = a;
        ListNode* tempb= b;
        while(tempa && tempb){
            tempc->next = tempa;
            tempa =tempa->next;
            tempc = tempc->next;

            tempc->next = tempb;
            tempb =tempb->next;
            tempc = tempc->next;
        }
        tempc->next = tempa;
        head = c->next;


    }
};
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