Background: In the popular online video game Path of Exile, there is a skill tree that players can allocate points to as they gain levels. The skill tree is essentially a connected graph where a node is coloured "on" or "off" depending on whether a player has allocated that point or not. A player may begin at one of fifteen fixed locations in the graph, called starting nodes, by allocating it to be "on" and may only allocate a new node if it is connected to a node that is "on". The subgraph of "on" nodes are the allocated points. There are several special nodes scattered across the graph which are called jewel nodes.
Definitions: A path connecting nodes $a$ and $b$ is a connected subset of nodes containing $a$ and $b$. Given a path $P$ connecting nodes $a$ and $b$, the length of $P$ between $a$ and $b$ is the minimum number of edges in any subpath of $P$ connecting $a$ and $b$.
Question: What is the longest path from a starting node to a jewel node?
That is, what is the maximum length of a path that begins at one of the starting nodes and ends at a jewel node? I would like an algorithm for computing such a path, but I don't know if such an algorithm exists. The graph is sufficiently large and complicated that a naive brute force search is probably not feasible.
Inspiration: This question was inspired by this Reddit question. There is an item in the game which provides greater bonuses to the player for longer paths, so it is natural to want to maximise these bonuses.
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