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Walkthrough and analysis
Check n=5, edges=[[0,1],[0,2],[0,3],[1,4]].
Edge count: 4 = 5 - 1. ✓
Build adjacency list: {0:[1,2,3], 1:[0,4], 2:[0], 3:[0], 4:[1]}.
DFS from 0. Visit: 0, 1, 4, 2, 3. Count = 5 = n. ✓
Return true.
For n=5, edges=[[0,1],[1,2],[2,3],[1,3],[1,4]]: 5 edges ≠ 4. Return false immediately.
Build adjacency: . DFS: . Total: time and space.
