Given n nodes labeled 0 to n-1 and a list of undirected edges, determine if these edges form a valid tree.
A valid tree has exactly n - 1 edges, is connected, and has no cycles.
With n = 5 and edges = [[0,1],[0,2],[0,3],[1,4]]:
- 5 nodes, 4 edges (n-1). ✓
- All nodes reachable from any node. ✓
- No cycles. ✓
- Valid tree. Return true.
With n = 5 and edges = [[0,1],[1,2],[2,3],[1,3],[1,4]]:
- 5 edges > 4. Has a cycle (1-2-3-1). Return false.
Constraints: .