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Graph Valid Tree
You're checking whether a set of connections forms a proper tree—one connected piece with no loops. It's a favorite in interviews because it forces you to articulate what makes a tree a tree, then verify those properties cleanly. The classic gotcha is accidentally detecting cycles when you revisit your parent node. Once you're comfortable here, connected-component problems become much easier.
Learn this pattern
Graph Interview Questions
BFS explores by layers using a queue; DFS explores deeply using a stack or recursion -- the same traversal with a different container. Choose BFS for shortest-path in unweighted graphs and "minimum steps," DFS for counting components, islands, and tree recursion.
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Graph Interview Questions gives you a useful next rep while you are still on your phone.