aoc2024/07/src/main.zig

// tedious and bad code but zig is mostly fine ig

const std = @import("std");

var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
const alloc = arena.allocator();

const test_data = @embedFile("test");
const input_data = @embedFile("input");

pub fn main() !void {
    const stdout = std.io.getStdOut().writer();

    const value1 = try run1(input_data);
    try stdout.print("{d}\n", .{value1});

    const value2 = try run2(input_data);
    try stdout.print("{d}\n", .{value2});
}

test "test input part 1" {
    std.debug.print("\n", .{});
    const value = try run1(test_data);
    std.debug.print("{d}\n", .{value});
    try std.testing.expectEqual(3749, value);
}

test "test input part 2" {
    std.debug.print("\n",.{});
    const value = try run2(test_data);
    std.debug.print("{d}\n", .{value});
    try std.testing.expectEqual(11387, value);
}

fn parseIntFromReader(reader: anytype) anyerror!u64 {
    const f = try reader.readByte();
    if (f < '0' or f > '9') return error.BadCharacter;
    var v: u64 = f - '0';
    while (true) {
        const c = try reader.readByte();
        if (c < '0' or c > '9') {
            break;
        } else {
            v = (v * 10) + (c - '0');
        }
    }
    return v;
}

fn run2(s: []const u8) !u64 {
    var total: u64 = 0;

    const Entry = struct {
        n: u64,
        nums: std.ArrayList(u64)
    };

    var entries = std.ArrayList(Entry).init(alloc);
    var s_fbs = std.io.fixedBufferStream(s);
    var s_reader = s_fbs.reader();
    l: while (true) {
        const err: anyerror!void = b: {
            const n = parseIntFromReader(s_reader) catch |e| break :b e;
            try s_fbs.seekBy(-1);
            if ((s_reader.readByte() catch |e| break :b e) != ':') break :b error.BadCharacter;
            var e: Entry = Entry {
                .n = n,
                .nums = std.ArrayList(u64).init(alloc)
            };
            while ((s_reader.readByte() catch |er| break :b er) != '\n') {
                const i = parseIntFromReader(s_reader) catch |er| break :b er;
                try s_fbs.seekBy(-1);
                try e.nums.append(i);
            }
            try entries.append(e);
        };
        _ = err catch |e| switch (e) {
            error.EndOfStream => { break :l; },
            else => return e
        };
    }

    var str_buf: [64]u8 = undefined;
    var str_buf_fbs = std.io.fixedBufferStream(&str_buf);
    var str_buf_writer = str_buf_fbs.writer();
    for (entries.items) |entry| {
        const nums: []u64 = entry.nums.items;
        std.debug.print("{}:", .{entry.n});
        for (nums) |i| {
            std.debug.print(" {}", .{i});
        }
        std.debug.print("\n",.{});

        const OP = enum { ADD, MUL, CAT };
        var ops: [32]OP = .{OP.ADD}**32;
        check: while (true) {
            var op_i: usize = 0;
            var v = nums[0];
            for (nums[1..]) |n| {
                switch (ops[op_i]) {
                    OP.ADD => v += n,
                    OP.MUL => v *= n,
                    OP.CAT => {
                        try str_buf_fbs.seekTo(0);
                        try std.fmt.formatInt(v, 10, std.fmt.Case.lower, .{}, &str_buf_writer);
                        try std.fmt.formatInt(n, 10, std.fmt.Case.lower, .{}, &str_buf_writer);
                        v = try std.fmt.parseInt(u64, str_buf[0..str_buf_fbs.pos], 10);
                    },
                }
                op_i += 1;
            }

            if (v == entry.n) {
                std.debug.print("good!\n",.{});
                total += entry.n;
                break :check;
            }

            var i: usize = 0;
            while (true) {
                switch(ops[i]) {
                    OP.ADD => ops[i] = OP.MUL,
                    OP.MUL => ops[i] = OP.CAT,
                    OP.CAT => { ops[i] = OP.ADD; i += 1; continue; }
                }
                if (i >= nums.len - 1) break :check;
                break;
            }
        }
    }

    total += 0;
    return total;
}

fn run1(s: []const u8) !u64 {
    var total: u64 = 0;

    const Entry = struct {
        n: u64,
        nums: std.ArrayList(u64)
    };

    var entries = std.ArrayList(Entry).init(alloc);
    var s_fbs = std.io.fixedBufferStream(s);
    var s_reader = s_fbs.reader();
    l: while (true) {
        const err: anyerror!void = b: {
            const n = parseIntFromReader(s_reader) catch |e| break :b e;
            try s_fbs.seekBy(-1);
            if ((s_reader.readByte() catch |e| break :b e) != ':') break :b error.BadCharacter;
            var e: Entry = Entry {
                .n = n,
                .nums = std.ArrayList(u64).init(alloc)
            };
            while ((s_reader.readByte() catch |er| break :b er) != '\n') {
                const i = parseIntFromReader(s_reader) catch |er| break :b er;
                try s_fbs.seekBy(-1);
                try e.nums.append(i);
            }
            try entries.append(e);
        };
        _ = err catch |e| switch (e) {
            error.EndOfStream => { break :l; },
            else => return e
        };
    }

    for (entries.items) |entry| {
        const nums: []u64 = entry.nums.items;
        std.debug.print("{}:", .{entry.n});
        for (nums) |i| {
            std.debug.print(" {}", .{i});
        }
        std.debug.print("\n",.{});

        var ops: u32 = 0;
        const op_mask = (@as(u32,1) << @intCast(nums.len - 1)) - 1;
        check: while (true) {
            var no = ops;
            var v = nums[0];
            for (nums[1..]) |n| {
                if (no & 1 == 1) {
                    v *= n;
                } else {
                    v += n;
                }
                no >>= 1;
            }

            if (v == entry.n) {
                std.debug.print("good!\n",.{});
                total += entry.n;
                break :check;
            }

            ops += 1;
            if (ops & op_mask == 0) {
                break :check;
            }
        }
    }

    total += 0;
    return total;
}