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This is a medium difficulty Coding & Algorithms question, commonly asked during Onsite rounds at Netflix.

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This question is commonly asked for Software Engineer candidates at Netflix during technical interviews.

Implement ordering and undo executor | Netflix Coding Question

Quick Overview

This question evaluates graph algorithm skills (topological ordering and cycle detection) and software design competencies related to command interfaces, undo semantics, and shared-state management.

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Part 2: Text Command Executor With Undo

Implement a simple command executor for text editing. The editor starts with an empty string and processes operations in order. Supported operations are: - `('append', s)`: append string `s` to the end - `('delete', k)`: delete the last `k` characters; if `k` is larger than the current length, delete everything - `('undo',)`: undo the most recent `append` or `delete` operation that has not already been undone; if there is nothing to undo, do nothing Return the final text after processing all operations.

Constraints

0 <= len(operations) <= 100000
The total number of characters across all appended strings is at most 200000
0 <= k <= 200000 for delete operations
Only the three supported command types will appear

Examples

Input: [('append', 'abc'), ('append', 'de'), ('delete', 3)]

Expected Output: 'ab'

Explanation: After appending 'abc' and 'de', the text is 'abcde'. Deleting the last 3 characters leaves 'ab'.

Input: [('append', 'hello'), ('delete', 2), ('append', 'y'), ('undo',), ('undo',)]

Expected Output: 'hello'

Explanation: The first undo removes the appended 'y'. The second undo restores the two deleted characters.

Input: [('undo',), ('append', 'a'), ('undo',), ('undo',)]

Expected Output: ''

Explanation: Undo on empty history does nothing. After appending 'a', one undo removes it, and the final undo still does nothing.

Input: [('append', 'abc'), ('delete', 5), ('undo',)]

Expected Output: 'abc'

Explanation: Deleting more characters than exist clears the text. Undo restores the deleted content.

Input: []

Expected Output: ''

Explanation: Edge case: no operations means the text stays empty.

Hints

Undo should reverse the most recent still-active command, so a stack is a natural fit.
For each executed command, store just enough information to reverse it later instead of storing the whole text every time.

Quick Overview