Practice Arena

Python Coding Challenges

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467 challenges 330 easy 120 medium 17 hard
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All Python Basics Strings & Text Lists & Arrays Dicts & Sets Functions & Closures OOP & Classes Data Structures & Algorithms Advanced Python Iterators & Generators Decorators & Context Managers Error Handling & Exceptions Regular Expressions Math & Number Theory Bit Manipulation Dynamic Programming Trees & Binary Trees Graphs & Graph Algorithms Recursion & Backtracking Greedy Algorithms Binary Search Two Pointers & Sliding Window Stacks & Queues Heaps & Priority Queues Linked Lists Matrix & 2D Arrays Datetime & Time Calculations Data Formats & Parsing SQL & SQLite Numpy & Vectorized Computing Cryptography & Hashing
Lists & Arrays easy

Rearrange Positives and Negatives

Write a function that rearranges a list in-place so all negative numbers come before non-negative numbers.

in-place two-pointers partition
+10 pts 15m
OOP & Classes medium

Linked list reversal

Implement a singly linked list and a function to reverse it in place.

linked-list OOP pointers
+28 pts 25m
Two Pointers & Sliding Window medium

Container With Most Water

Given an array of heights, find the maximum area between two vertical lines that can hold water.

two-pointers array maximization
+20 pts 25m
Two Pointers & Sliding Window hard

Trapping Rain Water

Given an array of non-negative integers representing an elevation map, compute how much water it can trap after raining.

array two-pointers water-trapping
+40 pts 30m
Two Pointers & Sliding Window medium

Sort Colors (Dutch National Flag)

Implement the Dutch National Flag algorithm to sort an array of 0, 1, 2 in one pass.

in-place two-pointers sorting
+20 pts 25m
Two Pointers & Sliding Window easy

Longest Substring Without Repeating Characters

Implement a function that returns the length of the longest substring without repeating characters.

strings sliding-window two-pointers
+10 pts 15m
Two Pointers & Sliding Window hard

Minimum Window Substring

Implement a sliding window algorithm to find the minimum window substring containing all characters of a given pattern.

sliding-window two-pointers strings
+45 pts 35m
Two Pointers & Sliding Window medium

Character Replacement Window

Given a string and a number k, find the length of the longest substring that can be made uniform by replacing at most k characters.

sliding-window two-pointers strings
+30 pts 25m
Two Pointers & Sliding Window medium

Permutation in String

Determine if any permutation of a shorter string appears as a contiguous substring in a longer string using an efficient sliding window.

sliding-window two-pointers hash-map
+25 pts 25m
Two Pointers & Sliding Window medium

Count Nice Subarrays

Given an array of integers, count the number of contiguous subarrays that contain exactly k odd numbers.

sliding-window two-pointers subarray
+25 pts 25m
Two Pointers & Sliding Window hard

Subarrays with K different ints

Count the number of contiguous subarrays that contain exactly K distinct integers.

sliding-window two-pointers hashmap
+40 pts 40m

Showing 11 challenges

Guide: free Python coding challenges

Practice Python by solving problems

PythonSkillset challenges are hands-on coding exercises from beginner to advanced. Open a challenge, read the problem, write Python in the split-pane editor, and run tests with Pyodide — no install required.

How to use the arena

  1. Pick a category — basics, algorithms, strings, and more
  2. Open a challenge, read the statement, and edit the starter code
  3. Run tests, fix failures, then try a related quiz or tutorial lesson

Challenges vs tutorials and quizzes

Challenges test what you can build under constraints. For guided teaching, use our Python tutorials. For quick checks, try quizzes or copy snippets from code samples.