adventofcode2025/day8/zig/main.zig

const std = @import("std");

const Box = struct { x: i64, y: i64, z: i64, circuit: usize };

const Pair = struct { p1: usize, p2: usize, dist: i64 };

const CONNECTIONS = 100;

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();

    var stdin_buffer: [1024]u8 = undefined;
    var stdin_reader = std.fs.File.stdin().reader(&stdin_buffer);

    const stdin = &stdin_reader.interface;

    const allocator = gpa.allocator();
    var boxes = try std.ArrayList(Box).initCapacity(allocator, 1);
    defer boxes.deinit(allocator);

    var counter: usize = 0;

    while (try stdin.takeDelimiter('\n')) |line| {
        const line_trimmed = std.mem.trim(u8, line, "\n");
        var it = std.mem.splitScalar(u8, line_trimmed, ',');

        const x = try std.fmt.parseInt(i64, it.next().?, 10);
        const y = try std.fmt.parseInt(i64, it.next().?, 10);
        const z = try std.fmt.parseInt(i64, it.next().?, 10);

        try boxes.append(allocator, Box{ .x = x, .y = y, .z = z, .circuit = counter });
        counter += 1;
    }

    var pairs = try std.ArrayList(Pair).initCapacity(allocator, 1);
    defer pairs.deinit(allocator);

    for (boxes.items, 0..) |box1, i| {
        for (boxes.items[i + 1 ..], i + 1..) |box2, j| {
            const d = distance(box1, box2);

            try pairs.append(allocator, Pair{ .p1 = i, .p2 = j, .dist = d });
        }
    }

    std.mem.sort(Pair, pairs.items, {}, pair_sort);

    for (0..CONNECTIONS) |i| {
        const p1 = pairs.items[i].p1;
        const p2 = pairs.items[i].p2;

        const c1 = boxes.items[p1].circuit;
        const c2 = boxes.items[p2].circuit;

        // Both
        if (c1 == c2) {
            continue;
        }

        // Different circuits
        // Switch every box from circuit c2 to c1
        for (boxes.items) |*box| {
            if (box.circuit == c2) {
                box.circuit = c1;
            }
        }

        // Check if we are a single circuit
        const first = boxes.items[0].circuit;
        var found = false;
        for (boxes.items) |box| {
            if (box.circuit != first) {
                found = true;
                break;
            }
        }
        if (!found) {
            std.debug.print("{d}\n", .{ boxes.items[p1].x * boxes.items[p2].x });
            break;
        }
    }

    var circuits = try std.ArrayList(usize).initCapacity(allocator, 1);
    defer circuits.deinit(allocator);

    for (0..boxes.items.len) |_| {
        try circuits.append(allocator, 0);
    }

    for (boxes.items) |box| {
        circuits.items[box.circuit] += 1;
    }

    std.mem.sort(usize, circuits.items, {}, comptime std.sort.desc(usize));

    var task1: usize = 1;
    for (0..3) |i| {
        task1 *= circuits.items[i];
    }

    //    for (0..boxes.items.len) |i| {
    //        for (0..boxes.items.len) |j| {
    //            std.debug.print("{d}", .{adjacency.items[i].items[j]});
    //        }
    //        std.debug.print("\n", .{});
    //    }

    std.debug.print("{d}\n", .{task1});
}

fn pair_sort(_: void, p1: Pair, p2: Pair) bool {
    return p1.dist < p2.dist;
}

fn distance(p1: Box, p2: Box) i64 {
    return (p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y) + (p1.z - p2.z) * (p1.z - p2.z);
}