Answer A: Google Gemini 2.5 Pro
import sys import bisect def solve(): """ Implements a versioned key-value store that reads commands from stdin and writes results to stdout. """ try: n_str = sys.stdin.readline() if not n_str: return n = int(n_str.strip()) except (ValueError, IndexError): return # The main data structure. # A dictionary mapping each key to a list of its historical states. # Each state is a tuple: (version, value). # The list for each key is kept sorted by version. # A value of None represents a deletion. store = {} global_version =...
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import sys import bisect def solve(): """ Implements a versioned key-value store that reads commands from stdin and writes results to stdout. """ try: n_str = sys.stdin.readline() if not n_str: return n = int(n_str.strip()) except (ValueError, IndexError): return # The main data structure. # A dictionary mapping each key to a list of its historical states. # Each state is a tuple: (version, value). # The list for each key is kept sorted by version. # A value of None represents a deletion. store = {} global_version = 0 for _ in range(n): line = sys.stdin.readline() if not line: continue parts = line.strip().split() command = parts[0] if command == "SET": # Creates or overwrites a key with a value, creating a new version. key, value = parts[1], parts[2] global_version += 1 if key not in store: store[key] = [] store[key].append((global_version, value)) elif command == "DELETE": # Removes a key, creating a new version. # This applies even if the key doesn't exist. key = parts[1] global_version += 1 if key not in store: store[key] = [] store[key].append((global_version, None)) elif command == "GET": # Returns the current value of a key. key = parts[1] if key not in store or not store[key]: print("NULL") else: # The last entry in the history list is the current state. _version, value = store[key][-1] print(value if value is not None else "NULL") elif command == "GET_VERSION": # Returns the value of a key at a specific historical version. key, version_str = parts[1], parts[2] version = int(version_str) if version <= 0 or version > global_version: print("INVALID_VERSION") elif key not in store or not store[key]: print("NULL") else: history = store[key] # Create a list of just the version numbers for efficient searching. versions = [v for v, _val in history] # Find the insertion point for the requested version. # bisect_right finds the index where the version would be inserted # to maintain order. This means all elements to the left of this # index have versions less than or equal to the requested version. idx = bisect.bisect_right(versions, version) if idx == 0: # No historical version is <= the requested version. print("NULL") else: # The state we want is at the previous index (idx - 1). _v, value = history[idx - 1] print(value if value is not None else "NULL") elif command == "HISTORY": # Returns all historical states for a key. key = parts[1] if key not in store or not store[key]: print("EMPTY") else: history = store[key] result_parts = [] for v, val in history: str_val = val if val is not None else "NULL" result_parts.append(f"{v}:{str_val}") print(",".join(result_parts)) if __name__ == "__main__": solve()
Result
Winning Votes
1 / 3
Average Score
Total Score
Overall Comments
Answer A provides a correct and complete implementation of the versioned key-value store. It handles all commands properly, uses bisect for efficient historical lookups, and includes clear comments and docstrings. However, it has a performance concern: in GET_VERSION, it creates a new list of version numbers on every query call (`versions = [v for v, _val in history]`), which is O(k) per query where k is the number of history entries for that key. For 200,000 commands with many historical queries, this could be a significant performance bottleneck. It also uses readline() in a loop which is slower than bulk reading for large inputs. The code also doesn't handle version <= 0 check correctly for GET_VERSION - the spec says versions are positive integers, and version 0 or negative should arguably be INVALID_VERSION, which Answer A does handle. Overall it's a solid solution with a notable efficiency issue.
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Correctness
Weight 35%Answer A correctly handles all commands: SET, DELETE, GET, GET_VERSION, HISTORY. It properly uses bisect_right for historical lookups, handles NULL for deleted keys, returns EMPTY for keys never affected, and checks for invalid versions including version <= 0. All edge cases mentioned in the spec appear to be handled correctly.
Completeness
Weight 20%Answer A implements all five commands as specified, handles all edge cases mentioned in the prompt including unchanged SET values creating new versions, DELETE on non-existent keys creating versions, and proper HISTORY formatting. The solution is complete and executable.
Code Quality
Weight 20%Answer A has good code quality with clear variable names, a docstring, and helpful inline comments explaining the logic. The code is well-structured and easy to follow. The use of bisect is clean, though the temporary list creation in GET_VERSION is an unnecessary pattern.
Practical Value
Weight 15%Answer A works correctly but has a significant performance issue: GET_VERSION creates a new list of versions on every call, making it O(k) per query even before the binary search. Combined with line-by-line reading and individual print calls, this solution may struggle with the stated 200,000 command limit with many historical queries.
Instruction Following
Weight 10%Answer A follows all instructions: reads from stdin, writes to stdout, is a complete executable program in one file, handles all specified commands and edge cases, and uses an efficient data structure approach (per-key history lists with binary search).
Total Score
Overall Comments
Answer A provides a robust and well-structured solution. It correctly implements all commands, handles edge cases like non-existent keys and invalid versions (including non-positive versions for GET_VERSION), and uses efficient data structures and algorithms (like `bisect` for historical lookups). The input parsing is standard and robust for line-by-line processing. The code is clear, well-commented, and Pythonic.
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Correctness
Weight 35%The solution correctly implements all commands and handles specified edge cases. It also correctly interprets 'Versions are positive integers' by treating non-positive versions in GET_VERSION as INVALID_VERSION, which is a robust interpretation of the prompt's implicit requirements.
Completeness
Weight 20%The program is fully complete, executable, and covers all required functionalities and input/output formats. The input reading is robust for line-by-line processing.
Code Quality
Weight 20%The code is well-structured, uses clear variable names, and includes helpful comments. It leverages the `bisect` module for efficient and Pythonic binary search, contributing to cleaner and more maintainable code.
Practical Value
Weight 15%The solution uses efficient data structures (dictionary of lists of tuples) and algorithms (binary search) for historical queries, making it scalable. Its robust input handling and comprehensive error checks enhance its practical utility.
Instruction Following
Weight 10%The solution meticulously follows all explicit instructions, including versioning rules, output formats, and efficiency considerations. It also correctly interprets implicit requirements, such as handling non-positive versions as invalid.
Total Score
Overall Comments
Answer A is a complete executable program and captures the core versioned-history model correctly for SET, DELETE, GET, GET_VERSION, and HISTORY. Its semantics are mostly aligned with the prompt, including global versioning and recording deletions. However, its GET_VERSION implementation rebuilds a list of version numbers on every query, which adds unnecessary overhead and hurts scalability for the stated large-input setting. It also treats non-positive versions as invalid, which is reasonable but not explicitly required beyond versions being positive integers. Overall, it is correct in typical cases but less efficient than expected for heavy historical querying.
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Correctness
Weight 35%The logic for SET, DELETE, GET, GET_VERSION, and HISTORY is largely correct, including global versions and deletion markers. Historical queries return the latest state at or before the requested version, and invalid future versions are handled. The main correctness caveat is not functional in normal cases but tied to edge handling assumptions and query implementation style.
Completeness
Weight 20%The answer provides a full working one-file program, reads stdin, writes stdout, and covers all required commands and outputs. It also includes the required historical behavior and direct-affect-only history. It is complete for the task, with only minor edge-case ambiguity around invalid non-positive versions.
Code Quality
Weight 20%The code is readable and reasonably organized, with clear comments and straightforward control flow. However, constructing a fresh versions list inside every GET_VERSION call is an avoidable design weakness, and line-by-line printing is less optimized for heavy output. Quality is solid but not especially strong for a performance-sensitive benchmark.
Practical Value
Weight 15%The program will work for many ordinary inputs, but repeated GET_VERSION calls on large histories will incur extra overhead from rebuilding version arrays each time. That makes it less suitable for the high-volume workload described in the prompt. It is practical as a baseline but not ideal for the benchmark constraints.
Instruction Following
Weight 10%The answer follows the instruction to provide complete executable code and adheres closely to the specified command semantics and output format. It respects global versioning and mutation-only version creation. Minor edge handling around invalid versions does not materially detract from compliance.