Complete Screening Guide

The Complete Guide to Passing Toptal

150+ problems organized by category, covering all 4 rounds of Toptal's technical screening. Deep theory, full C# solutions, step-by-step traces, edge cases, and mock tests. With a structured 60-day study plan and ~120 hours of practice, you'll be ready to be in the 7.4% who pass.

150+
Problems
13
Categories
4
Rounds Covered
17
Codility Lessons
3
Mock Tests
C#
All Solutions
01

Quick Start

Choose your starting point based on where you are in the process.

New to Toptal?
Start here. Understand all 4 rounds, pass rates, and the 60-day study plan.
Strategy Overview
Ready to Practice?
Jump into problems. Start with Arrays & Prefix Sums — the most tested category.
Start Problems
Test Tomorrow?
Quick-reference cheatsheet with pattern recognition, templates, and edge cases.
Cheatsheet
02

60-Day Study Path

You have 60 days — that's a huge advantage. Follow this 8-week plan at ~2 hours/day. 120 total hours of structured practice. See the full daily breakdown in the Strategy Overview.

Week 1 (Days 1–7): Foundations
Strategy & Golden Rules Arrays & Prefix Sums Codility Lessons 1-5
Week 2–3 (Days 8–21): Core Patterns
Hash Maps & Sets Sliding Window & Two Pointers Sorting & Binary Search Stacks & Queues Mock Test 1 (Day 21)
Week 4–5 (Days 22–35): Data Structures Deep Dive
Linked Lists Trees & BST Graphs & BFS/DFS Codility Lessons 6-17 (all 100%) Mock Test 2 (Day 35)
Week 6–7 (Days 36–49): Algorithm Paradigms
Dynamic Programming Greedy Algorithms Strings & Pattern Matching Bit Manipulation & Math Intervals & Matrix Mock Test 3 (Day 49)
Week 8+ (Days 50–60): Polish, Mock Tests & All 4 Rounds
Pattern Cheatsheet Review Mock Tests 4 & 5 Communication Round Prep Live Coding (REACTO) Take-Home Project Guide
⚠
Critical Rule: O(n) = 100% score. O(n²) on n=100,000 = timeout = 50% score. Always find the optimal complexity.
03

All 4 Rounds

Toptal has 4 sequential rounds. You must pass each to proceed.

Round 1
Communication Interview
15-30 min video call. English fluency, motivation, experience, hourly rate. Common questions with model answers.
26.4% pass15-30 min
Round 2
Codility Test (90 min)
3 algorithmic problems, auto-graded. Need ~210/300. This is where 92.6% fail. The entire problem bank prepares for this.
7.4% pass90 min
Round 3
Live Coding Interview
2 problems, 40 min, screen shared. REACTO method, communication matters as much as code.
3.6% pass40 min
Round 4
Take-Home Project
Build a project in 2 weeks. Clean Architecture, DI, tests, Docker. Then code review with senior dev.
3.2% pass2 weeks
04

13 Problem Categories

150+ problems organized by technique. Each with full C# solution, step-by-step trace, edge cases, and complexity analysis.

Category 1
Arrays & Prefix Sums
MissingInteger, GenomicRangeQuery, MaxCounters, Kadane's, Product Except Self, and more.
15 problemsMost Tested
Category 2
Sliding Window & Two Pointers
Longest Substring, Container With Water, 3Sum, Trapping Rain Water, MinAvgTwoSlice.
15 problemsHigh Frequency
Category 3
Sorting & Binary Search
Rotated arrays, Merge Intervals, Kth Largest, MinMaxDivision, NailingPlanks.
15 problemsEssential
Category 4
Hash Maps & Sets
Group Anagrams, Top K Frequent, Longest Consecutive, LRU Cache, Subarray Sum K.
15 problemsGo-To Optimization
Category 5
Stacks & Queues
Brackets, Fish, StoneWall, Monotonic Stack, Largest Rectangle, Basic Calculator.
15 problemsCodility Favorite
Category 6
Graphs & BFS/DFS
Number of Islands, Course Schedule, Dijkstra, Word Ladder, Union-Find, Alien Dictionary.
15 problemsAdvanced
Category 7
Greedy Algorithms
Jump Game, Gas Station, Task Scheduler, Partition Labels, Interval scheduling.
12 problems
Category 8
Dynamic Programming
Coin Change, LIS, Edit Distance, Knapsack, Stock with Cooldown, Palindromic Substring.
15 problemsHardest Category
Category 9
Trees & BST
Validate BST, LCA, Level Order, Path Sum, Serialize/Deserialize, Kth Smallest.
12 problems
Category 10
Strings & Pattern Matching
Palindromes, KMP, Wildcard Matching, Decode Ways, Minimum Window Substring.
12 problems
Category 11
Linked Lists
Reverse, Merge, Cycle Detection, Palindrome, Add Two Numbers, Merge K Lists.
10 problems
Category 12
Bit Manipulation & Math
XOR tricks, Sieve of Eratosthenes, Fast Exponentiation, Brian Kernighan's.
10 problems
Category 13
Intervals & Matrix
Merge Intervals, Spiral Matrix, Rotate Image, Flags, CountTriangles.
10 problems
05

Supplementary Resources

Essential guides for Codility mastery, mock testing, and interview preparation.

Must Complete
Codility 17 Lessons Guide
All 17 Codility lessons with key techniques, optimal solutions, and 100% score checklist. Rule #1 of passing.
17 lessonsCritical
Practice
3 Mock Tests (90 min)
Timed simulations with Easy + Medium + Hard problems. Collapsible hints and full solutions.
9 problems270 min total
Quick Reference
Pattern Recognition Cheatsheet
35+ pattern signals, complexity lookup, edge cases, 10 copy-paste C# templates, test day checklist.
35+ patterns10 templates
Round 3
Live Coding — REACTO Method
Framework for live interviews: Repeat, Examples, Approach, Code, Test, Optimize. Communication templates.
2 walkthroughs
Round 4
Take-Home Project Guide
Clean Architecture, DI, Repository pattern, Unit Tests, Docker, Swagger. Full example project structure.
Complete guide
✅
Your goal: Score 210/300 on the Codility test. That means 100 on Easy + 100 on Medium + at least 10 on Hard. Master Easy and Medium so you finish them in 40 minutes, leaving 50 minutes for Hard.