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IMC·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Apr 2026

Summary

IMC quant engineer interview with a graph theory true/false question that sounds deceptively simple but has a real gotcha buried in it.

Questions Asked (1)

Q1

True or false: given N nodes, an acyclic undirected graph has at most N-1 edges. Explain your reasoning.

Algorithms & Data Structures
Author's notes

My first instinct was to say true and move on because that's the tree property everyone knows.

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AI HintsAI Generated

Suggested Approach

State that the statement is true, then provide a proof using induction or the fact that a forest with N nodes and C components has N-C edges. Also, connect it to the concept of a tree having exactly N-1 edges.

Pro tip: Mention that this property is fundamental in graph theory and is used in algorithms like Kruskal's for cycle detection. Showing awareness of practical applications demonstrates deeper understanding.

1. Clarify definitions

Define acyclic undirected graph (forest) and note that a tree is a connected acyclic graph.

2. State the answer

Clearly state that the statement is true: an acyclic undirected graph with N nodes has at most N-1 edges.

3. Provide proof

Use induction: start with N=1 (0 edges), add a node and at most one edge to maintain acyclicity, or use the formula for a forest: edges = N - components ≤ N-1.

4. Discuss equality condition

Explain that equality holds if and only if the graph is connected (i.e., a tree).

5. Mention applications

Briefly note that this property is used in cycle detection and minimum spanning tree algorithms.

Key Points to Mention

  • Definition of acyclic undirected graph (forest)
  • A tree with N nodes has exactly N-1 edges
  • A forest with N nodes and C components has N-C edges
  • Proof by induction or using components
  • Equality holds when the graph is connected
  • Relevance to algorithms like Kruskal's or DFS for cycle detection

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.