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Trees, Graphs, and Recursion
Recursion and backtracking; binary trees and traversals (DFS pre/in/post, BFS level order); BSTs and heaps; graph representations and BFS/DFS; weighted-graph algorithms (Dijkstra, topological sort).
Module Content
Recursion & Backtracking
The mental model: solve a smaller problem; combine. Backtracking adds 'undo' for exploring all possibilities. FIND_VIDEO: search 'recursion backtracking interview pattern explained' — recommended channel: NeetCode / Abdul Bari. Aim for 12 min or under.
Quiz: Recursion and Backtracking Templates
How to write any recursive function: base case + recursive case. The backtracking template that solves subsets, permutations, combinations.
Binary Trees & Traversals
Pre-order, in-order, post-order, level-order. The four traversals you'll be asked about in every tree problem. FIND_VIDEO: search 'binary tree traversal DFS BFS interview' — recommended channel: NeetCode / Abdul Bari. Aim for 11 min or under.
Quiz: Tree Traversal Patterns
DFS vs BFS, the three DFS orderings, and when each is the right tool for a tree problem.
Mock 3 — Trees (60 min)
Practice four tree problems in the downloadable Jupyter notebook. Complete the functions, tests, recurrence and complexity notes, and required diagram or trace, then submit the notebook.
Binary Search Trees & Heaps
BST: ordered tree, O(log N) operations. Heap: complete tree for priority queue, O(log N) push/pop. FIND_VIDEO: search 'binary search tree heap priority queue interview' — recommended channel: NeetCode / Abdul Bari. Aim for 10 min or under.
Quiz: BST and Heap Mental Models
When you need ordered traversal — BST. When you need top-K or 'always the min/max' — heap.
Graphs: Representation & BFS/DFS
Adjacency list vs matrix. BFS for shortest unweighted path; DFS for connectivity and exploration. FIND_VIDEO: search 'graph BFS DFS representation interview' — recommended channel: NeetCode / William Fiset. Aim for 12 min or under.
Quiz: Graph Representation and Traversal
The three ways to represent a graph; when BFS beats DFS; the patterns for grid/matrix problems treated as graphs.
Graph Algorithms (Dijkstra, Topological Sort)
Weighted shortest path (Dijkstra) and dependency ordering (topo sort). The two named algorithms most likely to appear. FIND_VIDEO: search 'dijkstra topological sort algorithm explained' — recommended channel: NeetCode / Abdul Bari. Aim for 11 min or under.
Quiz: Dijkstra and Topological Sort
Both algorithms come up regularly. Templates and the problem signals that trigger each.
Mock 4 — Graphs (60 min)
Practice four graph and grid problems in the downloadable Jupyter notebook. Complete the functions, tests, algorithm-choice notes, and complexity analysis, then submit the notebook.