00Open for typing
Hello, Keys
Variables, loops, functions and conditionals
Variables and expressions / Conditionals / Loop accumulators / State in a loop / Helper functions
0 / 30 solved
easy · LEVEL 0
New to coding? The optional Foundation lessons can help.
A SMALL ADVENTURE IN BIG IDEAS.
The Iwons Path.
Nine chapters. One very curious typist.
Start small, find the patterns, and follow the ink.
01Open for typing
Typebars
Arrays and strings
Adjacent array positions / String runs / Stable array filtering / Nested array traversal / String scanning
0 / 50 solved
easy · LEVEL 1
02Open for typing
Card Catalog
Maps, sets, counting and sorting
Frequency maps / Set membership / Set intersection / Map grouping / Comparator sorting
0 / 50 solved
easy · LEVEL 2
03Open for typing
Two Fingers
Two pointers, windows and prefix sums
Opposite-end pointers / Read and write pointers / Fixed sliding windows / Variable sliding windows / Prefix range subtraction / Two sorted streams
0 / 55 solved
medium · LEVEL 3
04Open for typing
Paper Stack
Stacks, queues, deques and simulations
Stack cancellation / Monotonic stacks / Queue simulation / Monotonic deques / Stack history
0 / 45 solved
medium · LEVEL 4
05Open for typing
Carriage Return
Recursion, sorting, binary search and bits
Divide-and-conquer recursion / Merge sort / Binary search boundaries / Binary search on answers / Bit counting / Prefix bit state
0 / 55 solved
medium · LEVEL 5
06Open for typing
Chain and Tree
Linked lists, binary trees and search trees
Linked traversal / Linked pointer reversal / Fast and slow pointers / Tree preorder / Tree breadth-first traversal / BST range pruning
0 / 55 solved
medium · LEVEL 6
07Open for typing
Switchboard
Graphs, heaps, union-find and tries
Graph breadth-first distances / Topological queues / Priority-queue shortest paths / Binary heaps / Union-find components / Trie prefix counts / Graph depth-first components
0 / 70 solved
hard · LEVEL 7
08Open for typing
Master Printer
Greedy choices, dynamic programming and backtracking
Greedy interval selection / Counting dynamic programming / Unbounded dynamic programming / Zero-one knapsack / Sequence DP with binary search / Interval dynamic programming / Backtracking choices / Backtracking with occupancy / Scheduling DP and binary search
0 / 90 solved
hard · LEVEL 8