Practice Reorder List

Read the task, work through the examples, and check your approach against the constraints. Use the original LeetCode task for coding and submissions.

Medium#143

LeetCode Problem

Reorder List

Linked List Two Pointers Stack Recursion

Problem Statement

For a singly linked list L0 -> L1 -> ... -> Ln, rearrange its nodes into L0 -> Ln -> L1 -> L(n-1) -> L2 -> L(n-2) -> ... . Change next pointers only; do not replace node values. Update the original list. Practice approach: Find the midpoint with slow and fast pointers, disconnect and reverse the second half, then weave the two halves together. Terminate the final next pointer to avoid a cycle. This uses O(n) time and O(1) extra space.

Source: Reorder List on LeetCode. Use the original task for its coding environment and submissions.

Examples

# 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 list contains between 1 and 50000 nodes.

1 <= Node.val <= 1000

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