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Design stack with O(1) minimum query | Anthropic Coding Question

Quick Overview

This question evaluates understanding of stack-based data structures, constant-time operation constraints, and handling edge cases such as empty queries, duplicate entries, and negative values.

hard
Anthropic
Coding & Algorithms
Software Engineer

Design stack with O(1) minimum query

Company: Anthropic

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: hard

Interview Round: Technical Screen

Design a stack-like data structure that supports the following operations, each in **O(1)** time: - `push(x)`: push integer `x` onto the stack - `pop()`: remove the top element (assume it’s non-empty when called) - `top()`: return the top element - `getMin()`: return the minimum value currently in the stack ### Requirements - All operations must be **worst-case O(1)**. - The stack may contain duplicate values. ### Clarifications to address - What should happen if `getMin()` is called on an empty stack? (Specify an approach: error/exception/sentinel.) - Are negative values allowed? (Assume yes.)

Quick Answer: This question evaluates understanding of stack-based data structures, constant-time operation constraints, and handling edge cases such as empty queries, duplicate entries, and negative values.

Implement a stack that supports the following operations in O(1) time each: - push(x): Push integer x onto the stack - pop(): Remove the element on top of the stack (no return value) - top(): Return the top element of the stack, or None if the stack is empty - min(): Return the minimum element currently in the stack, or None if the stack is empty You are given a sequence of operations. Execute them in order and return a list of results for only the operations that produce output (top and min). Note: pop does NOT produce output.

Constraints

1 <= len(operations) <= 2 * 10^5
For 'push', -10^9 <= value <= 10^9
Each operation must run in O(1) time
pop on an empty stack should do nothing

Examples

Input: ([('push', 5), ('push', 2), ('push', 2), ('min', None), ('pop', None), ('min', None), ('top', None)],)

Expected Output: [2, 2, 2]

Explanation: After pushing 5,2,2: min=2. Pop removes top 2, min remains 2, top is 2.

Input: ([],)

Expected Output: []

Explanation: No operations produce output.

Input: ([('min', None), ('top', None), ('pop', None), ('push', -1), ('min', None), ('top', None)],)

Expected Output: [None, None, -1, -1]

Explanation: min/top on empty return None. pop on empty does nothing. After push -1, min/top are -1.

Input: ([('push', 3), ('push', 1), ('push', 2), ('min', None), ('pop', None), ('min', None), ('pop', None), ('min', None), ('top', None)],)

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Quick Overview

Design stack with O(1) minimum query

Constraints

Examples

Hints