In-Memory Database with Backup and Restore

Problem: In-Memory Database with Backup and Restore Design and implement a simplified in-memory database that supports read/write on key-values and also supports backup and restore. Data Model Each record is identified by a unique string key. Each record contains multiple fields, where each field name is a string field. Each field maps to an integer value. Operations (processed in order) Process a sequence of commands and output results for specific commands. SET key field value Set field under key to integer value. Create key or field if they do not exist. No output. GET key field If the value exists, print the integer; otherwise print NULL. DELETE key field Remove field under key. If key has no remaining fields, remove the key as well. No output. BACKUP backup_id Save a full snapshot of the current database state under string id backup_id. If backup_id already exists, overwrite it. No output. RESTORE backup_id Restore the database state to the snapshot identified by backup_id. If backup_id does not exist, do nothing. No output. I/O Format First line: integer Q (#commands). Next Q lines: one command per line. Print one line per GET command. Constraints 1 <= Q <= 2 * 10^5 key/field/backup_id contain lowercase letters and digits, length 1..20 value fits in 32-bit signed int Should run efficiently (near O(Q) or O(Q log Q)). Example Input 10 SET a x 1 GET a x BACKUP b1 SET a x 2 GET a x RESTORE b1 GET a x DELETE a x GET a x RESTORE b2 Output 1 2 1 NULL