Algorithms & Data Structures

See the pattern before you solve it.

Core interview patterns, each anchored to a mnemonic and a worked TypeScript solution. Study the signal, then recall the shape until naming the pattern is instant.

32 patterns · 8 categories

Scanning & Windows

Sweep the array with moving pointers.6 patterns

The Executioner halves it every time.

Two knights close from both ends.

A glass pane slides across the counter.

An accountant's running receipt.

Interval Problems

Overlapping calendars, sorted & stapled.

Sorted Matrix Search

The Climber starts at the corner and never backtracks.

Stacks, Queues & Heaps

Order and priority over a stream.5 patterns

A teetering stack of plates.

Monotonic Stack

Bottles racked in strict order.

A first-come-first-served line.

Heap / Priority Queue

A bouncer keeps only the top K.

Coupled carriages, forward only.

Trees & Recursion

Branch, recurse, and combine.5 patterns

Tree DFS · Preorder

Stamp the node on arrival, then descend.

Tree DFS · Inorder

Left wing, sign the door, right wing — values come out sorted.

Tree DFS · Postorder

Clear both children first, then the parent — results bubble up.

Light every level before the next.

Try a path, then undo every step.

Graphs & Networks

Nodes, edges, and the paths between.7 patterns

Down each tunnel to its dead end.

Signal ripples outward, ring by ring.

A merchant ropes islands together.

Topological Sort

Fit each part before what needs it.

Always extend the cheapest route first.

Distance spreads across cells.

Minimum Spanning Tree

Connect every island as cheaply as possible.

Dynamic Programming

Remember solved subproblems.3 patterns

1D Dynamic Programming

Every answer already filed away.

Pack the sack for maximum worth.

2D Dynamic Programming

A grid of solved decisions.

Hashing & Sets

Constant-time lookup, counts, and membership.2 patterns

Hash Map Counting

Every key has a labeled drawer.

A guard recognizes every forbidden token.

Sorting & Selection

Order first, then exploit the order.2 patterns

Sweep chaos into useful order.

Partition until the target rank is fixed.

Strings & Tries

Prefixes, characters, and word paths.2 patterns

Each letter opens the next branch.

String Matching

Match characters without re-reading the hallway.