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Data Structures in Python: An Interview Refresher (Coderust)   Introduction to Graphs - Challenge 7: Check if Given Graph is Tree or not?


About the Introduction to Graphs - Challenge 7: Check if Given Graph is Tree or not? category (1)
I'm confused when comparing challenge 7 to challenge 3, why does challenge 3 need to use a recursive function on every vertex (line9-line11) to detect a cycle while challenge 7 doesn't? (1)