#588 · #2477 · Minimum Fuel Cost to Report to the Capital(到达首都的最少油耗)

There is a tree of n cities with city 0 as the capital. roads[i] = [a, b] is an undirected road. Each city has one representative, and each car has seats seats. Representatives travel toward the capital, and cars can share seats only when travelling together. Return the minimum total fuel cost, where each unit of distance costs 1 litre. Constraints: 1 <= n <= 10^5, 1 <= seats <= 10^5.