ransom note

reasoning_gym/algorithmic/ransom_note.py

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+"""Check if you can construct a ransom note from letters in a magazine.
+
+A popular Leetcode problem:
+https://leetcode.com/problems/ransom-note/description/
+"""
+
+from collections import defaultdict
+from dataclasses import dataclass
+from random import Random
+from typing import Optional
+
+from ..factory import ProceduralDataset, register_dataset
+
+MAX_NOTE_LENGTH = 100_000
+MAX_MAGAZINE_LENGTH = 100_001
+
+QUESTION_TEMPLATE = """Given two strings representing a ransom note and a magazine, return True if you can construct the ransom note using the letters in the magazine, and False otherwise.
+
+Each letter in the magazine string can only be used once in your ransom note.
+
+Ransom note: {ransom_note}
+Magazine: {magazine}
+"""
+
+
+@dataclass
+class RansomNoteConfig:
+    """Configuration for Ransom Note dataset generation"""
+
+    max_note_length: int = 10  # Maximum length of the ransom note
+    max_magazine_length: int = 30  # Maximum length of the magazine
+    p_solvable: float = 0.5  # Probability that the ransom note can be constructed
+
+    size: int = 500  # Virtual dataset size
+    seed: Optional[int] = None
+
+    def validate(self):
+        """Validate configuration parameters"""
+        assert 1 <= self.max_note_length <= MAX_NOTE_LENGTH, "max_note_length must be between 1 and MAX_NOTE_LENGTH"
+        assert (
+            2 <= self.max_magazine_length <= MAX_MAGAZINE_LENGTH
+        ), "max_magazine_length must be between 2 and MAX_MAGAZINE_LENGTH"
+        assert self.max_note_length < self.max_magazine_length, "max_note_length must be less than max_magazine_length"
+        assert 0 <= self.p_solvable <= 1, "p_solvable must be between 0 and 1"
+
+
+class RansomNoteDataset(ProceduralDataset):
+    """Generates Ransom Note exercises with configurable difficulty"""
+
+    def __init__(self, config: RansomNoteConfig):
+        super().__init__(config=config, seed=config.seed, size=config.size)
+        self.letters = {chr(i) for i in range(ord("a"), ord("z") + 1)}
+
+    def _get_inputs(self, rng: Random, solvable: bool) -> tuple[str, str]:
+        """Generate random ransom note and magazine"""
+        ransom_note_len = rng.randint(1, self.config.max_note_length)
+        ransom_note = [rng.choice(list(self.letters)) for _ in range(ransom_note_len)]
+
+        magazine_len = rng.randint(ransom_note_len, self.config.max_magazine_length)
+        magazine = ransom_note.copy()
+        if solvable:
+            magazine.extend([rng.choice(list(self.letters)) for _ in range(magazine_len - ransom_note_len)])
+        else:
+            remove_letter = rng.choice(magazine)
+            magazine.remove(remove_letter)
+            magazine.extend(
+                [rng.choice(list(self.letters - {remove_letter})) for _ in range(magazine_len - ransom_note_len + 1)]
+            )
+
+        rng.shuffle(ransom_note)
+        rng.shuffle(magazine)
+        return "".join(ransom_note), "".join(magazine)
+
+    def _can_construct(self, ransom_note: str, magazine: str) -> bool:
+        """Check if ransom note can be constructed from magazine"""
+        count = defaultdict(int)
+        for c in magazine:
+            count[c] += 1
+        for c in ransom_note:
+            if count[c] <= 0:
+                return False
+            count[c] -= 1
+        return True
+
+    def __getitem__(self, idx: int) -> dict:
+        """Generate a single Group Anagrams question"""
+        rng = Random(self.seed + idx)
+        solvable = rng.random() < self.config.p_solvable
+        ransom_note, magazine = self._get_inputs(rng, solvable)
+        answer = self._can_construct(ransom_note, magazine)
+
+        return {
+            "question": QUESTION_TEMPLATE.format(ransom_note=ransom_note, magazine=magazine),
+            "answer": str(answer),
+            "metadata": {"ransom_note": ransom_note, "magazine": magazine, "solution": answer, "solvable": solvable},
+        }
+
+
+register_dataset("ransom_note", RansomNoteDataset, RansomNoteConfig)