2025 day 8

adventofcode/2025/day8/day8.py

@@ -0,0 +1,77 @@
+#!/usr/bin/env python3
+import fileinput
+from itertools import combinations
+
+
+class UnionFind:
+    """
+    Two sets are called disjoint sets if they don't have any element in common.
+    The disjoint set data structure is used to store such sets. It supports
+    following operations:
+    - Merging two disjoint sets to a single set using Union operation.
+    - Finding representative of a disjoint set using Find operation.
+    """
+
+    def __init__(self, elements):
+        # init each element to be its own parent
+        self.parents = {e: e for e in elements}
+        # keep track of the size of each component
+        self.size = {e: 1 for e in elements}
+
+    def find(self, a):
+        if self.parents[a] != a:
+            self.parents[a] = self.find(self.parents[a])  # compress path
+        return self.parents[a]
+
+    def union(self, a, b):
+        ra, rb = self.find(a), self.find(b)
+        if ra == rb:
+            return
+        # attach smaller under larger (union by size)
+        if self.size[ra] < self.size[rb]:
+            ra, rb = rb, ra
+        self.parents[rb] = ra
+        self.size[ra] += self.size[rb]
+
+
+def distance(first, second):
+    xa, ya, za = first
+    xb, yb, zb = second
+    return (xa - xb) ** 2 + (ya - yb) ** 2 + (za - zb) ** 2
+
+
+def part1(boxes, edges, N=1000):
+    uf = UnionFind(boxes)
+    # make the first N connections
+    for _, a, b in edges[:N]:
+        uf.union(a, b)
+    sizes = sorted(uf.size.values(), reverse=True)
+    total = sizes[0] * sizes[1] * sizes[2]
+    return total
+
+
+def part2(boxes, edges):
+    uf = UnionFind(boxes)
+    for _, a, b in edges:
+        uf.union(a, b)
+        # if we've connected all the boxes, we're done
+        if max(uf.size.values()) == len(boxes):
+            xa, _, _ = a
+            xb, _, _ = b
+            return xa * xb
+
+
+def main(inp):
+    boxes = [tuple(map(int, line.split(","))) for line in inp]
+    edges = sorted((distance(a, b), a, b) for a, b in combinations(boxes, 2))
+    if len(boxes) == 20:  # example input
+        print("Part 1:", part1(boxes, edges, N=10))
+        print("Part 2:", part2(boxes, edges))
+    else:
+        print("Part 1:", part1(boxes, edges))
+        print("Part 2:", part2(boxes, edges))
+
+
+if __name__ == "__main__":
+    with fileinput.input() as f:
+        main(f)