Stack Questions at MakeMyTrip: What to Expect

Stack questions appear in roughly 12.5% of MakeMyTrip's technical interviews (3 out of 24 common problems). For a company managing flight bookings, hotel reservations, and complex itineraries, the stack's ability to handle nested operations, undo/redo states, and parsing sequences is directly relevant to real-world systems like back-navigation in a multi-step booking flow or validating layered discount codes.

What to Expect — Types of Problems

MakeMyTrip's stack problems typically focus on practical applications rather than abstract theory. You can expect two main categories:

1. Sequence Validation & Parsing: This includes classic problems like checking for balanced parentheses, tags, or brackets. This pattern is fundamental to validating structured data, such as ensuring the correct nesting of user-selected travel options (e.g., (flight + (hotel + transfer))).
2. Next Greater Element & Monotonic Stack Patterns: These problems involve finding the next larger or smaller element in an array. At scale, this algorithmic pattern is efficient for problems like finding the next available date with a lower fare in a time-series or managing price visibility in a sorted list.

You are unlikely to see highly complex stack variations; the focus is on clean implementation and recognizing the appropriate data structure.

How to Prepare — Study Tips with One Code Example

Master the core pattern: use a stack to track unmatched or pending elements while iterating through a sequence. The key is to push items onto the stack when you need to remember them for a future comparison, and pop them when a matching condition is met.

A fundamental example is validating a string containing just the characters (, ), {, }, [, and ]. The rule is that every opening bracket must have a corresponding closing bracket of the same type and in the correct nested order.

def isValid(s: str) -> bool:
    stack = []
    mapping = {')': '(', '}': '{', ']': '['}

    for char in s:
        if char in mapping:  # It's a closing bracket
            top_element = stack.pop() if stack else '#'
            if mapping[char] != top_element:
                return False
        else:  # It's an opening bracket
            stack.append(char)
    return not stack  # Valid if stack is empty

Recommended Practice Order

Build competency in this sequence:

1. Master the Fundamentals: Valid Parentheses (as above) and Next Greater Element I.
2. Handle Variations: Practice Minimum Add to Make Parentheses Valid and Asteroid Collision.
3. Apply to Strings: Solve Decode String and Remove All Adjacent Duplicates In String.
4. Simulate Real Processes: Finally, tackle Online Stock Span to understand how stack can track state over a sequence, analogous to tracking price changes over a booking timeline.

This progression solidifies the pattern before applying it to more scenario-based problems.

Practice Stack at MakeMyTrip