BFS

Level-order traversal, level averages, and right side view.

6 min readMastering Data Structures & Algorithms for Software Engineering InterviewsCode

Level-Order Traversal

BFS level-order traversal — watch the queue process each level

BFS Tree Traversal

Queue:1

Step 1 / 12 — Start: enqueue root (index 0)

BFS uses a queue. Process nodes level by level. Track level size to separate levels in result.

Golevel-order-traversal.go

23 linesLn 1, Col 1Go

Queue stores nodes. For each level, process exactly levelSize nodes. Children enqueued for next level.

Level-Based Problems

Problem	Approach
Level averages	Sum each level, divide by count
Right side view	Last node of each level (or first from right-to-left)
Left side view	First node of each level
Bottom-left value	Last level, first node (or reverse level order)
Min depth	First leaf encountered in BFS
Cousins check	Track parent and depth per level

BFS vs DFS

Aspect	BFS	DFS
Data structure	Queue	Stack (or recursion)
Order	Level by level	Deep first
Shortest path	Yes (unweighted)	No
Space	O(width) - max level size	O(height) - call stack
Use when	Shallow target, shortest path	Deep target, path to leaf

BFS for Shortest Path in Trees

In unweighted trees/graphs, BFS finds shortest path (minimum edges) because it explores all nodes at distance d before distance d+1. First time you reach target, that's the shortest path.

Mark this lesson complete to store local progress and unlock a cleaner resume path the next time you visit.