2025 Updated! Two Sigma OA Experience

Fresh out of Two Sigma's OA—let’s dive right into sharing the details! Timely interview experiences like this are gold for preparation, so if you’re gearing up for Two Sigma later, don’t miss this breakdown.

First, Key OA Basics

Test Date: October 12, 2025

Duration: 75 minutes

Question Count: 2 questions (1 focuses on logical reasoning, the other on computation + string manipulation)

Platform: HackerRank

Pro Tip: I used Programhelp’s low-profile co-session + voice timing reminders—more on how game-changing that was later.

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Deep Dive into Both Questions: From Prompt to Solution

(1) Question 1: Balanced Split String with Wildcards

This question seems tricky at first, but it gets simple once you clarify the logic. Don’t jump into complex stack-based solutions immediately—that’ll only confuse you.

Understanding the Prompt

Given a string containing (, ), [, ], and ?, split it into two non-empty, consecutive substrings (they must cover the entire original string with no overlaps).

Each substring can be rearranged into a balanced string after replacing ? (each ? can become any bracket type).

Your task is to count the number of valid split ways.

A balanced string means brackets must be properly matched and nested.

Examples: "([])" and "()[]" are valid, while "([)]" and "(()" are not.

Example

Input:

s = "[?(]??[?]"

There are 2 valid splits:

1. s1 = "[?(]", s2 = "??[?"

   • Replace ? in s1 with ) → rearranged as "()[]"
   • Replace ? in s2 with [] → rearranged as "[][]"

2. s1 = "[?(]??", s2 = "[?"

   • Replace ? in s1 to form "()[][]"
   • Replace ? in s2 with ] → "[]"

Answer: 2

Core Solution Logic

We check every possible split point (from 1 to len(s)-1). For each split, verify whether both substrings can become balanced by replacing ?.

To check a single substring:

1. Even length: Balanced strings must have pairs of brackets. Odd-length substrings are invalid.
2. Bracket count balance: For each bracket type (() and []), count the existing brackets and use ? to fill gaps.

For round brackets:

• Let left = number of '(', right = number of ')', and q = number of '?'
• We need to satisfy: |left - right| ≤ q (left + right + q) is even

Apply the same for square brackets.

Iterate through all split points with this logic for efficient checking (works up to length 1e5).

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(2) Question 2: Closest Pure Color

At first glance, this question looks intimidating, but it mainly tests computation and string manipulation.

Understanding the Prompt

Each color is a 24-bit integer composed of three 8-bit components:

• Red (R)
• Green (G)
• Blue (B) Each component is between 0 and 255.

Distance between two colors:
d = √[(r1 - r2)² + (g1 - g2)² + (b1 - b2)²]

You don’t need to compute the square root—compare squared distances to avoid floating-point errors.

Your task:
Compare a given pixel color to 5 pure colors (black, white, red, green, blue) and find the closest one.

If multiple colors share the same minimum distance, output "Ambiguous".

Pure Color RGB Values

Pure Color	R	G	B
Black	0	0	0
White	255	255	255
Red	255	0	0
Green	0	255	0
Blue	0	0	255

Step-by-Step Solution Example

Input:

n = 1

pixels = ["000000001111111100111100"]

Split the 24-bit binary string into 8-bit segments:

• R: "00000000" → 0
• G: "11111111" → 255
• B: "00111100" → 60

Pixel’s RGB = (0, 255, 60)

Compute squared distances:

• Green (0, 255, 0): (0-0)² + (255-255)² + (60-0)² = 3600
• Other pure colors have larger distances.

Result: "Green"

Key Notes

• Always group bits correctly in 8-bit segments.
• Compare squared distances only.
• Handle ties: if multiple colors have equal min distance, output "Ambiguous".

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Time Management & Pro Tips

Time Allocation

• 45 minutes on Question 1: logical reasoning and condition checks take time.
• 25 minutes on Question 2: focus on correctness and edge cases.

Don’t Fear Long Questions
Question 2’s length is misleading—once broken down, it’s easier than Question 1.

Mock Tests Matter
Two Sigma’s OA isn’t overly difficult, but precision matters. Practice mock tests to build pattern familiarity and stay calm during the real test.

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Final Takeaway

Two Sigma’s OA emphasizes logic clarity, implementation precision, and disciplined time management.

For Question 1, focus on length and bracket counts first—avoid overcomplicating with stacks.

For Question 2, detail orientation is key—binary parsing and tie-handling are where people slip.

If you’re targeting quantitative or trading firms like Two Sigma, Jane Street, or Citadel, preparation consistency is what pays off.

Whether you train independently or with a professional setup like Programhelp’s interview assistance, early preparation gives you an edge.

High-salary offers don’t come by luck—keep practicing, stay calm, and master the basics.

If you have questions about implementation or OA details, leave a comment below.