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Foundations
Beginner15 problemsThe Python you reach for every day — variables, control flow and the core data types.
- problem_01
Conditionals: letter grades
practices Conditionals
python~10 min+1 conceptStart solving - problem_02
Functions: FizzBuzz
practices Functions
python~10 min+2 conceptsStart solving - problem_03
Hello, World!
practices Your first program
python~5 minStart solving - problem_04
Say your name
practices Your first program
python~6 minStart solving - problem_05
Share the cookies
practices Numbers and arithmetic
python~7 minStart solving - problem_06
Shopping total
practices Numbers and arithmetic
python~6 minStart solving - problem_07
Variables: storing values
practices Variables and types
python~8 min+1 conceptStart solving - problem_08
*args/**kwargs: tally the lot
practices Flexible function arguments
python~15 min+1 conceptStart solving - problem_18
Dicts: counting words
practices Dictionaries
python~12 min+2 conceptsStart solving - problem_19
Errors: safe divide
practices Errors and exceptions
python~10 min+1 conceptStart solving - problem_23
Lists: top N values
practices Lists
python~12 min+1 conceptStart solving - problem_24
Loops: sum the even numbers
practices Loops
python~12 min+2 conceptsStart solving - problem_29
Sets: unique, sorted
practices Tuples and sets
python~10 min+2 conceptsStart solving - problem_30
Slicing: rotate right by k
practices Slicing
python~12 min+1 conceptStart solving - problem_33
Strings: valid palindrome
practices Strings
python~12 min+2 conceptsStart solving
Idioms & Objects
Beginner+14 problemsWrite it the Pythonic way — comprehensions, sorting, recursion, classes and generators.
- problem_11
Classes: bank account
practices Classes and objects
python~15 min+1 conceptStart solving - problem_13
Comprehensions: squares of evens
practices Comprehensions
python~10 min+1 conceptStart solving - problem_16
Dataclasses: build a leaderboard
practices Dataclasses
python~15 min+2 conceptsStart solving - problem_17
Decorators: count the calls
practices Decorators
python~15 min+2 conceptsStart solving - problem_37
f-strings: format a receipt
practices String formatting
python~15 min+1 conceptStart solving - problem_21
Higher-order: filter then map
practices Higher-order functions
python~12 min+1 conceptStart solving - problem_38
itertools: running maximum
practices The itertools module
python~15 min+1 conceptStart solving - problem_26
Regex: pull out the numbers
practices Regular expressions
python~15 min+1 conceptStart solving - problem_59
collections: group the words
practices The collections module
python~15 min+2 conceptsStart solving - problem_41
Context managers: build a Capture
practices Context managers
python~20 min+1 conceptStart solving - problem_60
functools: memoized Fibonacci
practices The functools module
python~20 min+1 conceptStart solving - problem_45
Generators: running totals
practices Iterators and generators
python~14 min+1 conceptStart solving - problem_53
Recursion: deep sum
practices Recursion
python~14 min+1 conceptStart solving - problem_54
Sorting: by frequency
practices Sorting
python~15 min+2 conceptsStart solving
Data Structures
Intermediate28 problemsThe building blocks of fast solutions — hashing, stacks, trees, heaps and binary search.
- problem_09
Aggregate traffic by endpoint
practices Packets, addresses and protocols
python~15 min+1 conceptStart solving - problem_10
Build a capped retry schedule
practices Timeouts, retries and idempotency
python~15 min+1 conceptStart solving - problem_12
Clean sensor readings
practices Data cleaning and missing values
python~15 min+1 conceptStart solving - problem_14
Compute an order total
practices Input validation and pagination
python~15 min+1 conceptStart solving - problem_15
Count classifier outcomes
practices Model evaluation and error analysis
python~15 min+1 conceptStart solving - problem_20
Group sales by category
practices Data cleaning and missing values
python~15 min+1 conceptStart solving - problem_22
Keep one result per request
practices Timeouts, retries and idempotency
python~15 min+1 conceptStart solving - problem_25
Paginate an inventory
practices Input validation and pagination
python~15 min+1 conceptStart solving - problem_27
Repair an inventory balance
practices Problem decomposition
python~15 min+1 conceptStart solving - problem_28
Scale a feature column
practices Features and normalization
python~15 min+1 conceptStart solving - problem_31
Split a time-ordered dataset
practices Training, validation and leakage
python~15 min+1 conceptStart solving - problem_34
Summarize request latency
practices Distributions, averages and percentiles
python~15 min+1 conceptStart solving - problem_35
Trees: maximum depth
practices Trees and binary search trees
python~12 min+1 conceptStart solving - problem_36
Two pointers: valid palindrome
practices Two pointers
python~15 min+1 conceptStart solving - problem_39
Binary search: search insert position
practices Binary search
python~15 minStart solving - problem_48
Hashing: top K frequent elements
practices Hash maps and sets
python~20 min+1 conceptStart solving - problem_49
Hashing: two sum
practices Hash maps and sets
python~15 min+1 conceptStart solving - problem_50
Intervals: merge overlapping ranges
practices Intervals
python~20 min+1 conceptStart solving - problem_51
Linked lists: merge two sorted
practices Linked lists
python~16 min+1 conceptStart solving - problem_55
Stacks: valid parentheses
practices Stacks and queues
python~15 min+1 conceptStart solving - problem_56
Trees: count values in range
practices Trees and binary search trees
python~16 min+1 conceptStart solving - problem_57
Trees: in-order traversal
practices Trees and binary search trees
python~14 min+1 conceptStart solving - problem_58
Two pointers: pair sum in sorted array
practices Two pointers
python~15 minStart solving - problem_66
Heaps: kth largest element
practices Heaps / priority queues
python~18 min+1 conceptStart solving - problem_67
Monotonic stack: daily temperatures
practices Monotonic stack
python~25 min+1 conceptStart solving - problem_68
Prefix sums: subarrays summing to k
practices Prefix sums
python~20 min+1 conceptStart solving - problem_69
Sliding window: longest substring without repeating
practices Sliding window
python~20 min+2 conceptsStart solving - problem_70
Sliding window: minimum size subarray sum
practices Sliding window
python~22 min+1 conceptStart solving
Core Algorithms
Advanced12 problemsCrack real interview & contest problems — greedy, backtracking, DP and graph traversal.
- problem_42
DP: climbing stairs
practices Dynamic programming
python~18 min+1 conceptStart solving - problem_43
DP: house robber
practices Dynamic programming
python~20 min+1 conceptStart solving - problem_44
Dynamic programming: unique paths
practices Dynamic programming
python~20 minStart solving - problem_46
Greedy: jump game
practices Greedy algorithms
python~18 min+1 conceptStart solving - problem_47
Greedy: maximum subarray (Kadane)
practices Greedy algorithms
python~20 min+1 conceptStart solving - problem_61
Backtracking: all permutations
practices Backtracking
python~24 min+1 conceptStart solving - problem_62
Backtracking: all subsets
practices Backtracking
python~22 min+1 conceptStart solving - problem_63
DP: coin change
practices Dynamic programming
python~22 min+1 conceptStart solving - problem_64
DP: longest increasing subsequence
practices Dynamic programming
python~22 minStart solving - problem_65
Graphs: number of islands
practices Graphs
python~24 min+1 conceptStart solving - problem_71
Union-Find: number of provinces
practices Union-Find (Disjoint Set)
python~25 min+1 conceptStart solving - problem_72
BFS: shortest path in a grid
practices BFS and DFS
python~25 min+1 conceptStart solving
Advanced Algorithms
Expert3 problemsGo deeper — number theory, advanced graphs, segment trees and string matching.