Level 3Exercise #60

Undo recent edits

Apply 'undo' commands to the latest saved edit and return remaining edits.

What you’ll practice

This Level 3 exercise focuses on deque stack in the Collections curriculum. Solve the challenge prompt above using clear, idiomatic Python and the relevant language or standard-library tools.

Relevant Python reference: collections.deque.

Sample Test Cases

Example #1

Input:apply_undos(['type A','type B','undo'])

Output:['type A']

Reference Solution

Reveal Reference Solution

def apply_undos(commands: list[str]) -> list[str]:
    from collections import deque
    history = deque()
    for command in commands:
        if command == 'undo' and history:
            history.pop()
        elif command != 'undo':
            history.append(command)
    return list(history)

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Undo recent edits

What you’ll practice

Sample Test Cases

Further Reading

Reference Solution