Reorder List
Medium
Linked List
Two Pointers
Stack
Recursion
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. You must do this **in-place** without altering the nodes' values.
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
Time Complexity
O(n)
Space Complexity
O(1)
14
Case 1
Input: [1,2,3,4]
Expected: [1,4,2,3]
Case 2
Input: [1,2,3,4,5]
Expected: [1,5,2,4,3]
Case 3
Input: [1]
Expected: [1]