BFS on graph
Last updated: April 17, 2026
Quick Overview
Implement the Breadth-First Search (BFS) algorithm to traverse a given undirected graph represented as an adjacency list. Your function should return the nodes in the order they are visited, starting from a specified source node. Ensure your solution handles graphs with cycles and disconnected components.
Amazon
April 17, 202624
6
1,507 solved
Implement the Breadth-First Search (BFS) algorithm to traverse a given undirected graph represented as an adjacency list. Your function should return the nodes in the order they are visited, starting from a specified source node. Ensure your solution handles graphs with cycles and disconnected components.
Coding interviews at Amazon focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
What the Interviewer Expects
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- How would you modify your solution to handle streaming input?
- What happens if the input contains duplicates?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve the problem of traversing an undirected graph using BFS, we will utilize the BFS traversal pattern which is suitable here because it explores all neighbors at the present depth prior to movin...
Approach
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Initialize the Data Structures: We will use a queue to keep track of the nodes to visit and a set to track visited nodes to avoid processing a node more than once.
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**Start from the Source...
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