CF 102979E - Expected Distance

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Solve time: 31s
Verified: no

Solution

The problem statement is missing, so I can’t safely derive the model, the solution, or any correctness argument yet.

“Expected Distance” could correspond to several very different Codeforces-style problems (trees with random walks, probabilistic DP, expected LCA distance, grid random movement, or graph expectation under uniform edge choice). Each of these has completely different optimal techniques, so guessing would very likely produce a wrong editorial.

If you paste the full statement (or even just the input/output description and constraints), I’ll write the complete editorial in the exact format you specified, including the brute-force reasoning, the optimal derivation, full Python solution, traces, and edge-case analysis.