Swim in Rising Water
Find the minimum time needed to swim from the top-left to the bottom-right of a grid where water level rises and you can only move to cells with elevation ≤ current time.
Partition to k subsets
Determine if an array of positive integers can be partitioned into k subsets of equal sum using backtracking.
Remove invalid parentheses
Given a string with parentheses and letters, return all valid strings after removing the minimum number of invalid parentheses.
Hamiltonian Cycle Backtrack
Implement a backtracking algorithm to find a Hamiltonian cycle in an undirected graph.
Remove K Digits to Form the Smallest Number
Given a non-negative integer as a string, remove exactly k digits to form the smallest possible integer without leading zeros.
Patching Array
Given a sorted array of positive integers and a target n, find the minimum number of patches to make every number from 1 to n representable as a subset sum.
Median of Sorted Array BS
Implement a binary search algorithm to find the median of two sorted arrays efficiently.
Kth Smallest in Sorted Matrix
Implement kth_smallest(matrix, k) to return the kth smallest element in a row- and column-sorted square matrix.
Trapping Rain Water
Given an array of non-negative integers representing an elevation map, compute how much water it can trap after raining.
Minimum Window Substring
Implement a sliding window algorithm to find the minimum window substring containing all characters of a given pattern.
Subarrays with K different ints
Count the number of contiguous subarrays that contain exactly K distinct integers.
Minimum Window Subsequence
Given strings s and t, return the minimum window substring of s that contains t as a subsequence, or empty string if none exists.
Second node value
Return the second value or None if fewer than two nodes.
Drop the tail node
Return a new list without the last node.
Join node values with arrows
Format string node values as 'a -> b -> c'; empty list returns ''.
Insert value at index
Insert x at index i in a new list.
Compare two linked lists
Return True when both lists have identical values in order.
Index of maximum value
Return index of largest value (first on tie).
Add scalar to vector
Add constant k to every element of the vector.
Inclusive numeric range vector
Return [start, start+step, ...] through end inclusive.
Count elements in matrix
Return total scalar count.
Binarize vector at threshold
Return 1.0 where v[i] >= t else 0.0.
Showing 25–46 of 46 challenges · hard
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.