Interview Cake

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You want to be able to access the largest element in a stack.

You've already implemented this Stack class:

class Stack { // initialize an empty array to hold our stack items private $items = []; // push a new item onto the stack public function push($item) { $this->items[] = $item; } // remove and return the last item public function pop() { // if the stack is empty, return null // (it would also be reasonable to throw an exception) if (!count($this->items)) { return null; } return array_pop($this->items); } // return the last item without removing it public function peek() { if (!count($this->items)) { return null; } return $this->items[count($this->items) - 1]; } }

Use your Stack class to implement a new class MaxStack with a method getMax that returns the largest element in the stack. getMax should not remove the item.

Your stacks will contain only integers.

What if we push several items in increasing numeric order (like 1, 2, 3, 4...), so that there is a new max after each push? What if we then pop each of these items off, so that there is a new max after each pop? Your algorithm shouldn't pay a steep cost in these edge cases.

You should be able to get a runtime of for push, pop, and getMax.

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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.

time for push, pop, and getMax. additional space, where m is the number of operations performed on the stack.

Our solution requires additional space for the second stack. But do we really need it?

Can you come up with a solution that requires additional space? (It's tricky!)

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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.

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