Python coding challenges: "hashmap"

All Easy Medium Hard

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

Dicts & Sets easy

Pair with difference K

Count unordered index pairs with absolute difference exactly K, handling duplicates correctly.

dictionary set counting

+10 pts 15m

Dynamic Programming medium

Longest Arithmetic Subsequence

Given a list of integers, return the length of the longest arithmetic subsequence (constant difference) within it.

dp subsequence hashmap

+30 pts 25m

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 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

Heaps & Priority Queues medium

Top K Frequent Elements

Given an integer array and a number k, return the k most frequent elements using a heap-based approach.

heap frequency counting

+25 pts 25m

Showing 5 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

Pick a category — basics, algorithms, strings, and more
Open a challenge, read the statement, and edit the starter code
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.

Python Coding Challenges