Versioned User Follow Graph with Snapshots

Implement a system that maintains directed user-follow edges and supports queries against any historical snapshot. Initially, the graph has no edges. Process Q commands in order. Every FOLLOW or UNFOLLOW operation creates a new snapshot version. Version 0 is the initial empty graph. Commands FOLLOW u v Add directed edge u -> v to the current graph. If the edge already exists, the state is unchanged, but a new version is still created. UNFOLLOW u v Remove directed edge u -> v from the current graph. If the edge does not exist, the state is unchanged, but a new version is still created. FOLLOWS version u v Determine whether u follows v in historical version. Print true or false. FOLLOWERS version v Print all users that follow v in version, in ascending order. Print an empty line if there are no followers. Input Format The first line contains integer Q, followed by Q command lines. User IDs and version IDs are non-negative integers. Every queried version is guaranteed to exist. Constraints 1 <= Q <= 2 * 10^5 0 <= u, v <= 10^9 All historical versions must remain queryable and immutable. Example Input 8 FOLLOW 1 2 FOLLOW 3 2 FOLLOWS 1 1 2 FOLLOWERS 2 2 UNFOLLOW 1 2 FOLLOWS 2 1 2 FOLLOWS 3 1 2 FOLLOWERS 3 2 Output true 1 3 true false 3 Example Input 4 FOLLOW 1 2 FOLLOWS 1 1 2 UNFOLLOW 1 2 FOLLOWS 2 1 2 Output true false