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Hooray! It's opposite day. Linked lists go the opposite way today.

Write a function for reversing a linked list. Do it in place.

Your function will have one input: the head of the list.

Your function should return the new head of the list.

Here's a sample linked list node class:

class LinkedListNode { private $value; private $next = null; public function __construct($value) { $this->value = $value; } public function getNext() { return $this->next; } public function setNext($next) { $this->next = $next; } public function getValue() { return $this->value; } public function setValue($value) { $this->value = $value; } }

We can do this in space. So don't make a new list; use the existing list nodes!

We can do this is in time.

Careful—even the right approach will fail if done in the wrong order.

Try drawing a picture of a small linked list and running your function by hand. Does it actually work?

The most obvious edge cases are:

  1. the list has 0 elements
  2. the list has 1 element

Does your function correctly handle those cases?

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Where do I enter my password?

Actually, we don't support password-based login. Never have. Just the OAuth methods above. Why?

  1. It's easy and quick. No "reset password" flow. No password to forget.
  2. It lets us avoid storing passwords that hackers could access and use to try to log into our users' email or bank accounts.
  3. It makes it harder for one person to share a paid Interview Cake account with multiple people.

time and space. We pass over the list only once, and maintain a constant number of variables in memory.

This in-place reversal destroys the input linked list. What if we wanted to keep a copy of the original linked list? Write a function for reversing a linked list out-of-place.

Start your free trial!

Log in or sign up with one click to get immediate access to free mock interview questions

Where do I enter my password?

Actually, we don't support password-based login. Never have. Just the OAuth methods above. Why?

  1. It's easy and quick. No "reset password" flow. No password to forget.
  2. It lets us avoid storing passwords that hackers could access and use to try to log into our users' email or bank accounts.
  3. It makes it harder for one person to share a paid Interview Cake account with multiple people.

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