Example 1:
Input: ["CommandLog","execute","execute","execute","undo","undo","undo"]
[[],["A",["x"]],["B",["y"]],["C",["x","y"]],[null],["x"],["y"]]
Output: [null,null,null,null,"C","A","B"]
Explanation:
Example 2:
Input: ["CommandLog","execute","execute","execute","undo","undo","undo"]
[[],["alpha",[]],["beta",["prod"]],["gamma",[]],["prod"],[null],[null]]
Output: [null,null,null,null,"beta","gamma","alpha"]
Build a command log that supports normal undo and tag-filtered undo.
Implement the CommandLog class:
CommandLog() initializes an empty log.void execute(string command, string[] tags) appends a command with its tags. A command can have zero or more tags.string undo(string tag) removes and returns one command from the log.
tag is omitted (or null), undo the most recent command that is still active.tag.Additional rules:
Design the data structure so all operations remain efficient for up to 10^5 calls.
Undo with null removes the latest command overall (C). Then undoing by x returns A, and undoing by y returns B.
10^5 total calls to execute and undo.0 <= tags.length <= 10 for each execute call.1 <= command.length <= 100 and command is an opaque identifier.1 <= tag.length <= 20 when a non-null tag is provided.undo calls are valid (there is always a command that can be undone for that call).