Pass functions and analyze basic data structures

Q: Pass functions and analyze basic data structures

This question evaluates proficiency with higher-order functions, passing functions or delegates, closures, and reasoning about side effects, alongside the ability to analyze fundamental data structures and their performance characteristics.

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Use PracHub's coding console to write, test, and debug your solutions in Python or JavaScript. View hints, test against sample inputs, and compare with official solutions.

Q: What difficulty level is this coding question?

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

Q: What role is this question designed for?

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

Question

Implement a function applyTwice(f, x) that accepts a function f and a value x and returns f(f(x)) in your preferred language. Demonstrate how to pass functions (or delegates) as parameters and discuss closures and side effects. Then analyze arrays, linked lists, stacks, and queues: give time/space complexities for insert, delete, search, and iteration, and explain when you would choose each structure.

PracHub · Accepted Answer

from typing import List

def apply_twice(ops: List[str], x: int) -> int:
    def make_func(ops: List[str]):
        def f(val: int) -> int:
            for op in ops:
                parts = op.strip().split()
                if not parts:
                    continue
                name = parts[0]
                if name == 'add':
                    if len(parts) != 2:
                        raise ValueError('add expects 1 argument')
                    v = int(parts[1])
                    val += v
                elif name == 'mul':
                    if len(parts) != 2:
                        raise ValueError('mul expects 1 argument')
                    v = int(parts[1])
                    val *= v
                elif name == 'pow':
                    if len(parts) != 2:
                        raise ValueError('pow expects 1 argument')
                    e = int(parts[1])
                    if e < 0:
                        raise ValueError('pow exponent must be non-negative')
                    val = pow(val, e)
                elif name == 'neg':
                    val = -val
                elif name == 'abs':
                    val = abs(val)
                else:
                    raise ValueError(f'unknown operation: {name}')
            return val
        return f

f = make_func(ops)
    return f(f(x))

Construct a function f using a closure that captures the ops list. The inner function iterates over ops and applies each operation to the input value. Then compute f(f(x)) by invoking the constructed function twice. Parsing is done by splitting each operation string and handling the supported commands and their arguments. This approach demonstrates passing functions via closures while keeping operations pure and deterministic.

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