How do I approach Coding & Algorithms interview questions?

Coding & Algorithms questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master coding & algorithms interviews.

What difficulty level is this interview question?

This is a medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at Instacart.

What role is this question designed for?

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

Implement multiple coding round problems | Instacart Interview Question

Q: Implement multiple coding round problems

This multi-part question evaluates algorithmic problem-solving skills including efficient lookup/search, stable ordering and priority management, streaming algorithms under strict memory constraints, and expression parsing with variable substitution.

Solve the following coding problems.

1) Bus schedule (next departure)

Given:

A sorted list buses[] of bus departure times (minutes since 00:00).
A list arrivals[] of passenger arrival times (minutes since 00:00).

For each passenger, return the earliest bus departure time that is >= their arrival time, or -1 if no such bus exists.

Constraints:

1 <= len(buses), len(arrivals) <= 2e5
Times fit in 32-bit signed integers.

2) Priority boarding order

You are given a list of passengers. Each passenger has:

priority (smaller number = higher priority, e.g. 0 is best)
checkInTime (integer)
name (string)

Output the boarding order under these rules:

Higher priority boards first.
Within the same priority, earlier checkInTime boards first.
If still tied, preserve input order.

Follow-up: If passengers arrive as a stream, how would you produce the next passenger to board efficiently?

3) Decode passwords from a stream with limited reads

A file/stream contains multiple passwords encoded as (index, char) pairs in order of appearance. A password is defined by indices 0..L-1 appearing exactly once each, where L is the password length.

Rules:

The first password is guaranteed valid .
When parsing the stream, encountering an index that has already appeared in the current password indicates the start of the next password (i.e., the pair you just read belongs to the next password).
You cannot load the full file into memory. You may only read in chunks whose size is at most the length L of the first decoded password .

Return all decoded passwords in order.

4) Evaluate an arithmetic expression with up to two variables

Given:

A string expression expr containing integers, + and - , parentheses ( ) , optional whitespace, and variable names consisting of letters.
The expression contains at most two distinct variable names .
A map of variable values (e.g., {x: 3, y: 10} ), guaranteed to include any variables present.

Compute and return the integer result.

Note: You may not assume there are spaces between tokens.

Solve the following coding problems.

1) Bus schedule (next departure)

Given:

A sorted list buses[] of bus departure times (minutes since 00:00).
A list arrivals[] of passenger arrival times (minutes since 00:00).

For each passenger, return the earliest bus departure time that is >= their arrival time, or -1 if no such bus exists.

Constraints:

1 <= len(buses), len(arrivals) <= 2e5
Times fit in 32-bit signed integers.

2) Priority boarding order

You are given a list of passengers. Each passenger has:

priority (smaller number = higher priority, e.g. 0 is best)
checkInTime (integer)
name (string)

Output the boarding order under these rules:

Higher priority boards first.
Within the same priority, earlier checkInTime boards first.
If still tied, preserve input order.

Follow-up: If passengers arrive as a stream, how would you produce the next passenger to board efficiently?

3) Decode passwords from a stream with limited reads

Rules:

The first password is guaranteed valid .
When parsing the stream, encountering an index that has already appeared in the current password indicates the start of the next password (i.e., the pair you just read belongs to the next password).
You cannot load the full file into memory. You may only read in chunks whose size is at most the length L of the first decoded password .

Return all decoded passwords in order.

4) Evaluate an arithmetic expression with up to two variables

Given:

A string expression expr containing integers, + and - , parentheses ( ) , optional whitespace, and variable names consisting of letters.
The expression contains at most two distinct variable names .
A map of variable values (e.g., {x: 3, y: 10} ), guaranteed to include any variables present.

Compute and return the integer result.

Note: You may not assume there are spaces between tokens.

Implement multiple coding round problems

Quick Overview

1) Bus schedule (next departure)

2) Priority boarding order

3) Decode passwords from a stream with limited reads

4) Evaluate an arithmetic expression with up to two variables

Comments (0)

Implement multiple coding round problems

Quick Overview

1) Bus schedule (next departure)

2) Priority boarding order

3) Decode passwords from a stream with limited reads

4) Evaluate an arithmetic expression with up to two variables

Comments (0)