Implement a Simple Key-Value Store from Scratch

Implement a simple in-memory key-value store from scratch. Requirements Support operations: PUT key value: insert/overwrite GET key: return value; print NULL if missing DEL key: delete if present COUNT: print number of keys currently stored Input (stdin) First line: integer Q Next Q lines: one operation per line key and value are whitespace-free strings Output (stdout) Print one line per GET Print one line per COUNT Constraints 1 <= Q <= 2*10^5 key, value length 1..128 Aim for overall ~O(Q) time Example Input: 8 PUT a 1 PUT b 2 GET a DEL a GET a COUNT PUT c 3 COUNT Output: 1 NULL 1 2 Example Input 8 PUT a 1 PUT b 2 GET a DEL a GET a COUNT PUT c 3 COUNT Output 1 NULL 1 2