Virtually Cloneable Stacks

Implement a data structure VirtuallyCloneableStacks with the following methods

• VirtuallyCloneableStacks() which initializes an empty stack at index 0.
• copyPush(i) which clones the stack at index i, pushes an element to the clone, and then pushes the clone into the list of stacks.
• copyPop(i) which clones the stack at index i, pops an element from the clone, and then pushes the clone into the list of stacks.
• size(i) which returns the number of elements in stack at index i.

You can assume that each call will be valid. For example, a stack won’t be popped from an empty stack, and i will be in bounds.

Constraints

• 0 ≤ n ≤ 100,000 where n is the number of method calls.

https://binarysearch.com/problems/Virtually-Cloneable-Stacks

Examples

Example 1

Input

• methods = ['constructor', 'copyPush', 'copyPush', 'copyPop', 'size', 'size', 'size', 'size']
• arguments = [[], [0], [1], [2], [0], [1], [2], [3]]

Output

• answer = [None, None, None, None, 0, 1, 2, 1]

Explanation

s = VirtuallyCloneableStacks()
s.copyPush(0)
s.copyPush(1)
s.copyPop(2)
s.size(0) == 0
s.size(1) == 1
s.size(2) == 2
s.size(3) == 1

Solution