147Implement a dependency resolver using topological sorting

Package managers, build tools and module bundlers all need to know what to install or build first. Implement:

1. findOrder(numCourses, prerequisites) (LeetCode 210): prerequisites are pairs [a, b] meaning "take b before a". Return any order that takes every course, or [] if it is impossible (a cycle).
2. resolveInstallOrder(packages): packages maps a name to its dependency names, for example { app: ["react", "router"], router: ["react"], react: [] }. Return the install order (dependencies before dependents). Make it deterministic: when several packages are ready, take them in alphabetical order. Throw an Error:
   • Unknown dependency "x" required by "y" when a dependency is not in packages;
   • Circular dependency: a -> b -> a (the actual cycle path) when there is a cycle.