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C# coding challenges

226 challenges you can solve in C#, from first loops to graphs, dynamic programming and machine learning. Write your code in the browser, run the tests instantly and get an AI review.

Easy · 134 Medium · 68 Hard · 24

Skills you'll practise: CountingDigit extractionString splitting2D listsArithmeticFormulasListsLoopsConditionsDivisibilityFloating pointGradient descent
  • Python · C++ · C#
  • Automated tests
  • AI code review
  • Community solutions
Programming
Programming fundamentalsFrom variables to recursion, for beginners
AI and machine learning
AI Learning HubNeural networks, ML and LLMs from scratch Neural networks from scratchNeurons, backpropagation and optimizers Machine learning from scratchRegression, classification and clustering Transformers and LLMs from scratchTokenizers, attention and text generation Classical AI and reinforcement learningSearch, games and reinforcement learning
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226 challenges
Easy

Make an Array Nondecreasing

Find the fewest increments needed so each value is at least the previous one.

You'll learn Greedy fixesRunning maximum
ArraysGreedy
Python C++ C#
0 solved
No solutions yet
Easy

Remove Duplicates

Keep only the first occurrence of each value.

You'll learn Seen-value trackingOrder preservation
ArraysBeginnerSetsStudent-beginner
Python C++ C#
0 solved
No solutions yet
Medium

Minesweeper Neighbor Counts

Annotate a rectangular board.

You'll learn 8-neighbor checksBoundary handling
ArraysGrids
Python C++ C#
0 solved
No solutions yet
Medium

Smallest Missing Coin Sum

Find the first positive amount that cannot be made from the available coins.

You'll learn Reachable sumsSorting first
ArraysGreedy
Python C++ C#
0 solved
No solutions yet
Easy

Missing Number

Find the one number missing from 0..n.

You'll learn Arithmetic seriesSum difference trick
ArraysBeginnerStudent-beginnermath
Python C++ C#
0 solved
No solutions yet
Easy

Sum of Odd Numbers

Add every odd number up to a limit.

You'll learn For loopsAccumulators
BeginnerLearning-pathLoops
Python C++ C#
0 solved
No solutions yet
Easy

Armstrong Number

Check whether a number equals the sum of its digits raised to the digit count.

You'll learn Digit extractionPowers
BeginnerNumbersStudent-beginner
Python C++ C#
0 solved
No solutions yet
Medium

Longest Common Subsequence Length

A subsequence is formed by deleting zero or more elements while preserving the order of the remaining elements.

You'll learn 2D DP tablesMemory optimization
Dynamic-programmingSequences
Python C++ C#
0 solved
No solutions yet
Easy

Every Other Character

Keep the characters at even positions.

You'll learn String indexingSteps
BeginnerLearning-pathStrings
Python C++ C#
0 solved
No solutions yet
Hard

Hotel Room Allocation

Assign arriving groups in order.

You'll learn Range maximum queriesPoint updates
Segment-treesSimulation
Python C++ C#
0 solved
No solutions yet
Easy

DNA to RNA Transcription

Build an RNA string by replacing every DNA character with its partner.

You'll learn Character mappingTranslation tables
MappingStrings
Python C++ C#
0 solved
No solutions yet
Easy

Greatest Common Divisor

Find the largest number that divides both values.

You'll learn Euclid's algorithmModulo
BeginnerNumbersStudent-beginner
Python C++ C#
0 solved
No solutions yet
Easy

Triangle Classification

Classify three side lengths as invalid, equilateral, isosceles, or scalene.

You'll learn Triangle inequalityOrdering conditions
ConditionsGeometry
Python C++ C#
0 solved
No solutions yet
Medium

Two Nonattacking Knights

Count safe placements of two knights for each square board size.

You'll learn Counting placementsAttack patterns
Combinatoricsmath
Python C++ C#
0 solved
No solutions yet
Easy

Count Handshakes

Count handshakes when every pair of people shakes hands once.

You'll learn Counting pairsClosed formulas
Combinatoricsmath
Python C++ C#
0 solved
No solutions yet
Easy

Body Mass Index

Compute BMI from weight and height.

You'll learn FormulasFloating point
BeginnerLearning-pathVariables
Python C++ C#
0 solved
No solutions yet
Easy

Power by Repeated Multiplication

Raise a number to a power with a loop.

You'll learn Running productZero exponent
BeginnerLearning-pathLoops
Python C++ C#
0 solved
No solutions yet
Easy

Letter Grade

Turn a test score into a letter grade.

You'll learn if/elif chainsRanges
BeginnerConditionsLearning-path
Python C++ C#
0 solved
No solutions yet

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