Keys and Rooms

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Solution Guide: Keys and Rooms

Approach

Treat each room as a node and each key as a directed edge. DFS/BFS through keys and count visited nodes.

Complexity Analysis

Time
O(N + K)
Space
O(N)

Pattern

Graph Reachability

Why It Works

All possible moves are key edges. If every room is eventually visited, then keys connect the graph from node 0 to all nodes.

Updated Feb 2026