solved(python): baekjoon 1761

Author: himitery

baekjoon/python/1761/__init__.py

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+import sys
+from collections import defaultdict, deque
+from typing import cast
+
+read = lambda: sys.stdin.readline().rstrip()
+
+
+class Problem:
+    def __init__(self):
+        self.n = int(read())
+
+        self.nodes = defaultdict(set[tuple[int, int]])
+        for _ in range(self.n - 1):
+            src, dest, distance = map(int, read().split())
+            self.nodes[src].add((dest, distance))
+            self.nodes[dest].add((src, distance))
+
+        self.queries = [cast(tuple[int, int], tuple(map(int, read().split()))) for _ in range(int(read()))]
+
+        self.depth, self.parent, self.weights = self.make_tree()
+
+    def solve(self) -> None:
+        for x, y in self.queries:
+            print(self.weights[x] + self.weights[y] - 2 * self.weights[self.lca(x, y)])
+
+    def make_tree(self) -> tuple[list[int], list[list[int]], list[int]]:
+        queue, visited = deque([(1, 0)]), {1}
+        depth, parent, weights = (
+            [0 for _ in range(self.n + 1)],
+            [[0 for _ in range(20)] for _ in range(self.n + 1)],
+            [0 for _ in range(self.n + 1)],
+        )
+
+        while queue:
+            node, idx = queue.popleft()
+            depth[node] = idx
+
+            for child, distance in self.nodes[node]:
+                if child not in visited:
+                    queue.append((child, idx + 1))
+                    visited.add(child)
+                    parent[child][0] = node
+                    weights[child] = weights[node] + distance
+
+        for k in range(1, 20):
+            for node in range(1, self.n + 1):
+                parent[node][k] = parent[parent[node][k - 1]][k - 1]
+
+        return depth, parent, weights
+
+    def lca(self, x: int, y: int) -> int:
+        if self.depth[x] < self.depth[y]:
+            x, y = y, x
+
+        for k in range(20)[::-1]:
+            if self.depth[x] - (1 << k) >= self.depth[y]:
+                x = self.parent[x][k]
+
+        if x == y:
+            return x
+
+        for k in range(20)[::-1]:
+            if self.parent[x][k] != self.parent[y][k]:
+                x, y = self.parent[x][k], self.parent[y][k]
+
+        return self.parent[x][0]
+
+
+if __name__ == "__main__":
+    Problem().solve()

baekjoon/python/1761/main.py

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+[
+  {
+    "input": [
+      "7",
+      "1 6 13",
+      "6 3 9",
+      "3 5 7",
+      "4 1 3",
+      "2 4 20",
+      "4 7 2",
+      "3",
+      "1 6",
+      "1 4",
+      "2 6"
+    ],
+    "expected": [
+      "13",
+      "3",
+      "36"
+    ]
+  }
+]

baekjoon/python/1761/sample.json

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+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()