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Roadmap

A roadmap for data structures and algorithms

The 150 problems fall into 18 topics, drawn as 6 lines like a transit map. Ride each line from its first station, and change lines where a topic builds on one from another line.

Open the map in the appAll 150 problems

Foundations

The three basic containers, in order: an array, then one end of it (a stack), then nodes joined by pointers.

  1. Arrays & Hashing9 problems
  2. Stack6 problems
  3. Linked List11 problems

Search & scan

Two indexes over an array. A window is two pointers moving the same way, and binary search halves the range between them.

  1. Arrays & Hashing9 problems
  2. Two Pointers5 problems
  3. Sliding Window6 problems
  4. Binary Search7 problems

Trees

A tree node is a list node with two next pointers. A trie is a tree keyed by letters, and a heap is a tree packed into an array, which shortest paths need.

  1. Linked List11 problems
  2. Trees15 problems
  3. Tries3 problems
  4. Heap / Priority Queue7 problems
  5. Advanced Graphs6 problems

Graphs

Backtracking is a depth-first walk over a tree of choices. Graphs are the same walk when nodes can lead back, and weighted graphs arrive where the heap does.

  1. Trees15 problems
  2. Backtracking10 problems
  3. Graphs13 problems
  4. Advanced Graphs6 problems

Optimization

Dynamic programming is backtracking that remembers answers. Greedy is the case where one choice is always safe, and intervals are sorted, then swept greedily.

  1. Backtracking10 problems
  2. 1-D Dynamic Programming12 problems
  3. 2-D Dynamic Programming11 problems
  4. Greedy8 problems
  5. Intervals6 problems

Math & bits

It needs nothing past arrays, so it branches off the first station.

  1. Arrays & Hashing9 problems
  2. Math & Geometry8 problems
  3. Bit Manipulation7 problems