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Java coding challenges

225 challenges you can solve in Java, 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 · 67 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
226
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225 challenges
Medium

Q-Learning Updates

Apply the Q-learning update to a stream of experiences and watch rewards flow back to earlier states.

You'll learn Q-learningDiscounted rewards
Reinforcement learningaimachine learning
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
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Easy

Loss Functions: MSE, MAE and Cross-Entropy

Measure how wrong a model's predictions are with mean squared error, mean absolute error or binary cross-entropy.

You'll learn MSECross-entropy
Neural networksaimachine learning
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
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Easy

Pangram Check

A pangram contains every English letter at least once.

You'll learn Letter setsCase normalization
SetsStrings
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
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Medium

Forward Propagation in a Two-Layer Network

Run inputs through a hidden ReLU layer and a sigmoid output layer.

You'll learn Forward passMulti-layer networks
Neural networksaimachine learning
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
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Easy

Rotate Array

Rotate a list to the right by some steps.

You'll learn Array indexingModulo
ArraysBeginnerStudent-beginner
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
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Medium

Robot Command Simulator

Move a robot using L (turn left 90 degrees), R (turn right 90 degrees), and A (advance one step).

You'll learn Direction vectorsCommand processing
SimulationState-machines
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
No solutions yet
Easy

Single Artificial Neuron

Compute the output of one neuron: weighted sum of the inputs plus a bias, passed through sigmoid.

You'll learn NeuronsWeighted sums
Neural networksaimachine learning
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
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Easy

Title Case

Capitalize the first letter of every word.

You'll learn String methodsCapitalization
BeginnerStringsStudent-beginner
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
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Easy

Leap Year

Check whether a year follows the Gregorian leap-year rule.

You'll learn Boolean logicConditions
BeginnerNumbers
Python C++ C# Java JavaScript Go Rust Kotlin Swift
1 solved
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Easy

Count Words

Count the words in a sentence.

You'll learn String splittingWhitespace
BeginnerStringsStudent-beginner
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
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Easy

Reverse a String

Return the characters of a string in reverse order.

You'll learn Reverse iterationSlicing
BeginnerStringsStudent-beginner
Python C++ C# Java JavaScript Go Rust Kotlin Swift
1 solved
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Easy

Median of a List

Find the middle value of a list after sorting.

You'll learn SortingStatistics
Arraysmath
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
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Medium

Dense Layer Forward Pass

Compute the outputs of a fully connected layer of neurons with a choice of activation.

You'll learn Dense layersActivations
Neural networksaimachine learning
Python C++ C# Java JavaScript Go Rust Kotlin Swift
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# Java JavaScript Go Rust Kotlin Swift
0 solved
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Easy

Move Zeroes

Move every zero to the end while keeping the other order.

You'll learn Two pointersIn-place updates
ArraysBeginnerStudent-beginner
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
No solutions yet
Easy

Anagram Check

Check whether two phrases use the same letters.

You'll learn SortingFrequency counts
BeginnerStringsStudent-beginner
Python C++ C# Java JavaScript Go Rust Kotlin Swift
1 solved
View solutions (1)
Easy

Array Maximum

Find the largest value in a list.

You'll learn Tracking a maximumSingle pass
ArraysBeginnerStudent-beginner
Python C++ C# Java JavaScript Go Rust Kotlin Swift
0 solved
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Easy

Count Uppercase Letters

Count the capital letters in a text.

You'll learn Character checksCounting
BeginnerLearning-pathStrings
Python C++ C# Java JavaScript Go Rust Kotlin Swift
2 solved
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