Top 3 Graphs Interview Questions

Browse 3 real-world technical and behavioral interview questions about Graphs. Review scenarios, edge cases, and architectural best practices.

How do you decide between BFS and DFS - and how do you recognise a graph problem that nobody described as a graph?

Choose BFS when the question asks for the fewest steps in an unweighted graph or when you need results in distance order; choose DFS when you are asking a structural question such as connectivity, cycles or topological order, or when the graph is deep and narrow.

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Find the cheapest route between two nodes in a weighted directed graph. Then tell me what breaks if one edge has a negative weight.

Dijkstra fails with negative edges because it finalises the current cheapest node under the assumption that no later edge can reduce it. Use Bellman-Ford when negative edges are possible, and reject graphs with negative cycles. It also connects shortest paths to the point an interviewer is testing.

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You are given a set of tasks and their prerequisites. Produce a valid execution order, or report that none exists.

Topological sort produces an order only for a directed acyclic graph. Kahn's algorithm removes zero-in-degree nodes and detects a cycle when fewer than all nodes are emitted; DFS detects a cycle with a back edge into the active stack. Use this GRAPHS answer to show the decision, trade-off, and evidence rather than a memorised definition.

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