solved(python): baekjoon 13977

Author: himitery

baekjoon/python/13977/__init__.py

@@ -0,0 +1,40 @@
+import sys
+
+read = lambda: sys.stdin.readline().rstrip()
+
+
+class Problem:
+    def __init__(self):
+        self.n = int(read())
+        self.data = [tuple(map(int, read().split())) for _ in range(self.n)]
+
+        self.mod = 1_000_000_007
+
+    def solve(self) -> None:
+        factorial, inverse_factorial = self.precompute_factorial()
+
+        for n, r in self.data:
+            print(self.comb(factorial, inverse_factorial, n, r))
+
+    def precompute_factorial(self) -> tuple[list[int], list[int]]:
+        maximum = max(n for n, _ in self.data)
+        factorial, inverse_factorial = [1] * (maximum + 1), [1] * (maximum + 1)
+
+        for idx in range(1, maximum + 1):
+            factorial[idx] = factorial[idx - 1] * idx % self.mod
+
+        inverse_factorial[maximum] = pow(factorial[maximum], self.mod - 2, self.mod)
+        for idx in range(maximum - 1, -1, -1):
+            inverse_factorial[idx] = inverse_factorial[idx + 1] * (idx + 1) % self.mod
+
+        return factorial, inverse_factorial
+
+    def comb(self, factorial: list[int], inverse_factorial: list[int], n: int, r: int) -> int:
+        if r < 0 or r > n:
+            return 0
+
+        return factorial[n] * inverse_factorial[r] % self.mod * inverse_factorial[n - r] % self.mod
+
+
+if __name__ == "__main__":
+    Problem().solve()

baekjoon/python/13977/main.py

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+[
+  {
+    "input": [
+      "5",
+      "5 2",
+      "5 3",
+      "10 5",
+      "20 10",
+      "10 0"
+    ],
+    "expected": [
+      "10",
+      "10",
+      "252",
+      "184756",
+      "1"
+    ]
+  }
+]

baekjoon/python/13977/sample.json

@@ -0,0 +1,36 @@
+import json
+import os.path
+import unittest
+from io import StringIO
+from unittest.mock import patch
+
+from parameterized import parameterized
+
+from main import Problem
+
+
+def load_sample(filename: str):
+    path = os.path.join(os.path.dirname(os.path.abspath(__file__)), filename)
+
+    with open(path, "r") as file:
+        return [(case["input"], case["expected"]) for case in json.load(file)]
+
+
+class TestCase(unittest.TestCase):
+    @parameterized.expand(load_sample("sample.json"))
+    def test_case(self, case: str, expected: list[str]):
+        # When
+        with (
+            patch("sys.stdin.readline", side_effect=case),
+            patch("sys.stdout", new_callable=StringIO) as output,
+        ):
+            Problem().solve()
+
+            result = output.getvalue().rstrip()
+
+        # Then
+        self.assertEqual("\n".join(expected), result)
+
+
+if __name__ == "__main__":
+    unittest.main()