1. This problem can be reduced to the following: Given X, find two vertices such that path weight is equal to X. 2. It probably cannot be solved with naiive DP. Use centroid decomposition. 3. std::unordered_map gets TL while std::map gets AC.
When Ivan enters a project, *must* he use all the technologies used in the project, or can he choose to use only a subset of them (so as to avoid using a technology he has already used)?
