Valid parentheses
Return True if brackets in the string close in the correct order.
Binary search
Return the index of target in a sorted list, or -1 if not present.
Quicksort
Implement quicksort and return a sorted list.
BFS level-order traversal
Return the level-order traversal of a binary tree as a list of lists.
Graph DFS
Return all nodes reachable from a start node via DFS.
Longest increasing subsequence
Return the length of the longest strictly increasing subsequence.
Topological sort (Kahn)
Return a valid topological ordering of tasks, or [] if a cycle exists.
Word ladder length
Return the length of the shortest transformation from beginWord to endWord changing one letter at a time.
Index of peak element
Implement a function that returns the index of any peak element in a given integer array.
Find Peak Element
Implement a function that returns the index of any peak element in an integer array.
Median of Two Sorted Arrays
Given two sorted arrays, return the median of the combined sorted array in O(log(min(n,m))) time.
Pascal Triangle Row
Given a non-negative integer n, return the nth row of Pascal's triangle as a list of integers.
Merge Sort
Implement merge_sort(numbers) that returns a sorted copy of the input list using the merge sort algorithm.
Path Sum II All Paths
Return all root-to-leaf paths where the sum of node values equals a target.
Redundant Connection
Given a list of edges forming a tree plus one extra edge, return the edge that appears last in the input and creates a cycle.
Find Peak Index
Given a list of integers, return the index of any peak element where the value is not smaller than its neighbors.
Peak Element in Array
Implement a function that returns the index of any peak element in a list of integers.
K Closest Elements
Implement a function to return the k closest elements to a target in a sorted array.
Online Stock Span
Implement StockSpanner.next(price) that returns the maximum number of consecutive days (including today) with price <= current price.
Jump Search
Implement the jump search algorithm to locate a target in a sorted list, returning its index or -1.
AST Visitor Lite
Implement a depth-first traversal of a simplified AST and return identifier names in order.
Merge time intervals
Given a list of time intervals, merge all overlapping intervals and return the merged intervals.
Top N per group
Implement top_n_per_group that returns the top N scores for each group from a list of (group, score) pairs.
Consecutive available seats
Given a list of seat statuses, return the length of the longest consecutive run of available (0) seats.
Showing 1–24 of 29 challenges · Data Structures & Algorithms
Data Structures & Algorithms — Python coding challenges
What you will find here
This page lists data structures & algorithms challenges — real Python problems you solve in the browser IDE with instant test feedback. Each challenge includes a clear brief, starter code, and automated checks.
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.