adventofcode2025/day6/zig/main.zig

const std = @import("std");

const Operation = enum {
    multiplication,
    addition,
};

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

    var stdin_buffer: [4096]u8 = undefined;
    var stdin_reader = std.fs.File.stdin().reader(&stdin_buffer);

    const stdin = &stdin_reader.interface;

    const allocator = gpa.allocator();
    var operands = try std.ArrayList(std.ArrayList(u64)).initCapacity(allocator, 1);
    defer operands.deinit(allocator);

    var charmap = try std.ArrayList(std.ArrayList(u8)).initCapacity(allocator, 1);
    defer charmap.deinit(allocator);

    var operations = try std.ArrayList(Operation).initCapacity(allocator, 1);
    defer operations.deinit(allocator);

    var operand_num: u64 = 0;

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

        if (line[0] != '*' and line[0] != '+') {
            var charrow = try std.ArrayList(u8).initCapacity(allocator, 1);
            for (line) |char| {
                try charrow.append(allocator, char);
            }
            try charmap.append(allocator, charrow);
            var i: usize = 0;
            while (it.next()) |part| {
                const part_trimmed = std.mem.trim(u8, part, " ");

                if (part_trimmed.len == 0) {
                    continue;
                }

                const num = try std.fmt.parseInt(u64, part_trimmed, 10);

                if (operand_num == 0) {
                    const operand_list = try std.ArrayList(u64).initCapacity(allocator, 1);
                    try operands.append(allocator, operand_list);
                }

                try operands.items[i].append(allocator, num);
                i += 1;
            }
            operand_num += 1;
        } else {
            while (it.next()) |part| {
                const part_trimmed = std.mem.trim(u8, part, " ");

                if (part_trimmed.len == 0) {
                    continue;
                }

                const operation = switch (part_trimmed[0]) {
                    '*' => Operation.multiplication,
                    '+' => Operation.addition,
                    else => unreachable,
                };

                try operations.append(allocator, operation);
            }
        }
    }

    var task1: u64 = 0;

    for (operands.items, 0..) |operand_list, i| {
        const operation = operations.items[i];

        // Task1
        var result: u64 = if (operation == Operation.multiplication) 1 else 0;

        for (operand_list.items) |operand| {
            switch (operation) {
                Operation.addition => {
                    result += operand;
                },
                Operation.multiplication => {
                    result *= operand;
                },
            }
        }

        task1 += result;
    }

    var charcolumns = try std.ArrayList(std.ArrayList(u8)).initCapacity(allocator, 1);
    defer charcolumns.deinit(allocator);

    for (0..charmap.items[0].items.len) |_| {
        const charcolumn = try std.ArrayList(u8).initCapacity(allocator, 1);
        try charcolumns.append(allocator, charcolumn);
    }

    for (charmap.items) |charrow| {
        for (charrow.items, 0..) |char, j| {
            try charcolumns.items[j].append(allocator, char);
        }
    }

    var task2: u64 = 0;
    var operation_count: u32 = 0;

    var current_operation = operations.items[0];
    var result: u64 = if (current_operation == Operation.multiplication) 1 else 0;

    // Task2
    for (charcolumns.items, 0..) |charcolumn, i| {
        var empty = true;

        for (charcolumn.items) |char| {
            if (char != ' ') {
                empty = false;
                break;
            }
        }

        if (!empty) {
            const num = try std.fmt.parseInt(u64, std.mem.trim(u8, charcolumn.items, " "), 10);
            switch (current_operation) {
                Operation.addition => {
                    result += num;
                },
                Operation.multiplication => {
                    result *= num;
                },
            }
            if (i != charcolumns.items.len - 1) {
                continue;
            }
        }

        task2 += result;
        operation_count += 1;
        if (operation_count < operations.items.len) {
            current_operation = operations.items[operation_count];
            result = if (current_operation == Operation.multiplication) 1 else 0;
        }
    }

    for (operands.items) |*operand_list| {
        operand_list.deinit(allocator);
    }

    for (charcolumns.items) |*charcolumn| {
        charcolumn.deinit(allocator);
    }

    for (charmap.items) |*charrow| {
        charrow.deinit(allocator);
    }

    std.debug.print("{d}\n", .{task1});
    std.debug.print("{d}\n", .{task2});
}