Problem - Counting Paths - Read Statement

This problem extends distance queries. You need to count how many marked nodes appear on the path from $u$ to $v$. The path from $u$ to $v$ goes through their LCA. Split the problem: count marked nodes from $u$ to $lca(u, v)$, plus marked nodes from $v$ to $lca(u, v)$.

Subtract the LCA if it was counted twice. Think about how to preprocess the tree to answer "how many marked nodes are there from node $x$ up to the root?" in constant time.