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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
- 226
- Challenges
- 123
- Solutions shared
- 9
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All challenges
Search by topic, language, or difficulty.
Medium
Game of Life Step
Advance Conway's Game of Life by one generation.
You'll learn
Grid simulationNeighbor counting
No solutions yet
Hard
Shortest Delivery Tour
Visit every city once and return home as cheaply as possible.
You'll learn
Bitmask DPTraveling salesman
No solutions yet
Easy
Distance Between Points
Compute the straight-line distance between two points.
You'll learn
Pythagorean theoremSquare roots
Hard
Minimum Window Substring
Find the shortest piece of text containing all required characters.
You'll learn
Grow and shrink windowsFrequency maps
No solutions yet
Hard
Longest Path in a DAG
Find the heaviest path in a task dependency graph.
You'll learn
Topological orderDAG DP
No solutions yet
Medium
Gradebook Top Student
Find the student with the highest average score.
You'll learn
2D listsAverages
Medium
Count Islands
Count groups of connected land cells in a grid.
You'll learn
Flood fillRecursive DFS
Medium
K-th Smallest Element
Find the k-th smallest value without fully sorting.
You'll learn
QuickselectPartitioning
Hard
Median of Two Sorted Arrays
Find the median of two sorted lists combined.
You'll learn
Partition searchO(log n)
No solutions yet
Hard
Word Break
Decide whether text can be split into dictionary words.
You'll learn
Prefix DPString segmentation
Hard
Strongly Connected Components
Count groups of nodes that can all reach each other.
You'll learn
Graph algorithmsTarjan or Kosaraju
No solutions yet
Easy
Number Triangle
Build a triangle of increasing numbers.
You'll learn
Growing rowsCounters across rows
Easy
Prime Number Check
Decide whether a number is prime.
You'll learn
DivisibilityLoop optimization
Easy
Count Pairs With a Sum
Count pairs of positions whose values add up to a target.
You'll learn
Pairs of indexesAvoiding double counts
Hard
Largest Rectangle in a Histogram
Find the largest rectangle that fits under a histogram.
You'll learn
Monotonic stackArea calculation
No solutions yet
Hard
Course Schedule Order
Order courses so every prerequisite comes first.
You'll learn
Kahn's algorithmCycle detection
No solutions yet
Easy
Days in a Month
Return how many days a month has, including leap years.
You'll learn
Calendar rulesHelper functions
Medium
Tournament Standings
Rank teams from match records.
You'll learn
Aggregating resultsSorting with keys
No solutions yet
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