Skip to content
ı
Workspace
Workspace
Search anything…
⌘ K
Desk
Path
Problems
Review
More
PICK A CARD. FIND A PATTERN.
Read and write pointers
.
500 original challenges. Pick an index card and give it a go.
New problem
All problems
500
Bookmarked
My problems
Filters and order
1 active
Level
All
Level 0
Level 1
Level 2
Level 3
Level 4
Level 5
Level 6
Level 7
Level 8
Difficulty
All
Easy
Medium
Hard
Topic
All topics
Variables, loops, functions and conditionals
Variables and expressions
Conditionals
Loop accumulators
State in a loop
Helper functions
Arrays and strings
Adjacent array positions
String runs
Stable array filtering
Nested array traversal
String scanning
Maps, sets, counting and sorting
Frequency maps
Set membership
Set intersection
Map grouping
Comparator sorting
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
Stacks, queues, deques and simulations
Stack cancellation
Monotonic stacks
Queue simulation
Monotonic deques
Stack history
Recursion, sorting, binary search and bits
Divide-and-conquer recursion
Merge sort
Binary search boundaries
Binary search on answers
Bit counting
Prefix bit state
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
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
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
Status
Any
Solved
Attempted
Unsolved
Order
Path order
Title A–Z
Difficulty
STATUS
PROBLEM
DIFFICULTY
TOPIC
Duplicate carriage: Proof strip
Level 3 · Read and write pointers
Medium
Two pointers, windows and prefix sums
Read and write pointers
Duplicate carriage: Total receipt
Level 3 · Read and write pointers
Medium
Two pointers, windows and prefix sums
Read and write pointers
Duplicate carriage: Threshold file
Level 3 · Read and write pointers
Medium
Two pointers, windows and prefix sums
Read and write pointers
Duplicate carriage: First qualifying slip
Level 3 · Read and write pointers
Medium
Two pointers, windows and prefix sums
Read and write pointers
Duplicate carriage: Peak ticket
Level 3 · Read and write pointers
Medium
Two pointers, windows and prefix sums
Read and write pointers
Duplicate carriage: Floor ticket
Level 3 · Read and write pointers
Medium
Two pointers, windows and prefix sums
Read and write pointers
Duplicate carriage: Even-key census
Level 3 · Read and write pointers
Medium
Two pointers, windows and prefix sums
Read and write pointers
Duplicate carriage: Positive-ink invoice
Level 3 · Read and write pointers
Medium
Two pointers, windows and prefix sums
Read and write pointers
Duplicate carriage: Boss receipt
Level 3 · Read and write pointers
Medium
Two pointers, windows and prefix sums
Read and write pointers
9 of 500 problems
0 solved
Progress saved on this device
Not sure where to start? Try
the 30-day foundations plan
. One good problem at a time.