# [Solved] You are given the head of a singly linked-list. The list can be represented as: L0 → L1 → … → Ln – 1 → Ln Reorder the list to be on the following form: L0 → Ln → L1 → Ln – 1 → L2 → Ln – 2 → …

## Question

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

```L0 → L1 → … → Ln - 1 → Ln
```

Reorder the list to be on the following form:

```L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → …
```

You may not modify the values in the list’s nodes. Only nodes themselves may be changed.

Example 1:

```Input: head = [1,2,3,4]
Output: [1,4,2,3]
```

Example 2:

```Input: head = [1,2,3,4,5]
Output: [1,5,2,4,3]
```

Constraints:

• The number of nodes in the list is in the range `[1, 5 * 104]`.
• `1 <= Node.val <= 1000`

## Python Solution

```# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
def reorderList(self, head: ListNode) -> None:
"""
"""
return []

while fast and fast.next:
fast = fast.next.next
slow = slow.next

second_list = slow.next
slow.next = None

prev = None
curr = second_list

while curr:
nxt = curr.next
curr.next = prev
prev = curr
curr = nxt

second_list = prev

while second_list:
temp1 = first_list.next
temp2 = second_list.next
second_list.next = None
first_list.next = second_list
second_list.next = temp1
first_list = first_list.next.next
second_list = temp2 