Editorial for DMOPC '17 Contest 2 P3 - Bad Bunnies - Olympiads Online Judge

Editorial for DMOPC '17 Contest 2 P3 - Bad Bunnies

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Author: r3mark

For the first subtask, brute force to find the distance from each node to each rabbit. Then, check along the path from $X$ ~X~ to $Y$ ~Y~ to find the answer.

Time Complexity: $\mathcal O(RN)$ ~\mathcal O(RN)~

For the second subtask, compute the path from $X$ ~X~ to $Y$ ~Y~. Partition the tree by deleting the edges of the path. Several subtrees rooted from nodes on the path are created. Compute the minimum distance from each node of the path to a rabbit in its subtree using simple tree DP. The final answer is the minimum of these values.

Time Complexity: $\mathcal O(R+N)$ ~\mathcal O(R+N)~

Additional Challenge: How would you solve the problem if you were given $Q$ ~Q~ queries, the $i^\text{th}$ ~i^\text{th}~ of which has $X_i$ ~X_i~ and $Y_i$ ~Y_i~ as the start and endpoints, respectively, of the path?

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