Let me think about this problem. Codeforces contest 2237 problem H — I don't know this specific problem, but let me derive.
Slime occupies a connected set of m vertices in a tree. A move: remove one occupied vertex and add an unoccupied vertex, keeping connectivity and size m. Food appears sequentially at vertices; slime must occupy the vertex to eat. f = min moves to eat all foods in order, starting from initial set. Queries are online: each query appends a food vertex and asks total minimal moves.
Key: online with q up to 1e5, sum n 1e5. We need incremental computation.
Classic result: a connected set of size m in a tree is like a "subtree of size m". Moving it toward a target vertex v: cost to reach v = distance from v to the set (dist to nearest occupied vertex). Actually each move can shift the slime one step: remove a leaf of the occupied subtree, add adjacent vertex toward v. So cost to make v occupied = dist(v, S) where S is current set. But then subsequent foods depend on the resulting shape of S,