const std = @import("std");
const print = std.debug.print;

pub fn solve(part: []u8, buffer: []u8, allocator: std.mem.Allocator) !void {
    var lines = std.mem.splitScalar(u8, buffer, '\n');
    var left = std.ArrayList(usize).init(allocator);
    var right = std.ArrayList(usize).init(allocator);
    defer left.deinit();
    defer right.deinit();

    if (std.mem.eql(u8, part, "1")) {
        try part1(&lines, &left, &right, allocator);
    } else {
        try part2(&lines, &left, &right, allocator);
    }
}

fn part1(lines: *std.mem.SplitIterator(u8, .scalar), left: *std.ArrayList(usize), right: *std.ArrayList(usize), allocator: std.mem.Allocator) !void {
    while (lines.next()) |line| {
        if (line.len > 0) {
            var components = std.mem.split(u8, line, "   ");
            try left.append(try std.fmt.parseInt(usize, components.next().?, 10));
            try right.append(try std.fmt.parseInt(usize, components.next().?, 10));
        }
    }

    const left_s = try left.toOwnedSlice();
    const right_s = try right.toOwnedSlice();
    defer allocator.free(left_s);
    defer allocator.free(right_s);

    std.mem.sort(usize, left_s, {}, std.sort.asc(usize));
    std.mem.sort(usize, right_s, {}, std.sort.asc(usize));

    var sum: usize = 0;
    for (left_s, right_s) |item_l, item_r| {
        if (item_l > item_r) {
            sum += item_l - item_r;
        } else {
            sum += item_r - item_l;
        }
    }

    print("{d}\n", .{sum});
}

fn part2(lines: *std.mem.SplitIterator(u8, .scalar), left: *std.ArrayList(usize), right: *std.ArrayList(usize), allocator: std.mem.Allocator) !void {
    while (lines.next()) |line| {
        if (line.len > 0) {
            var components = std.mem.split(u8, line, "   ");
            try left.append(try std.fmt.parseInt(usize, components.next().?, 10));
            try right.append(try std.fmt.parseInt(usize, components.next().?, 10));
        }
    }

    const left_s = try left.toOwnedSlice();
    const right_s = try right.toOwnedSlice();
    defer allocator.free(left_s);
    defer allocator.free(right_s);

    std.mem.sort(usize, right_s, {}, std.sort.asc(usize));

    var map = std.AutoHashMap(usize, usize).init(allocator);
    defer map.deinit();

    var sum: usize = 0;
    for (left_s) |item_l| {
        sum += map.get(item_l) orelse blk: {
            var amount: usize = 0;
            for (right_s) |item_r| {
                if (item_l == item_r) {
                    amount += item_l;
                }
            }
            try map.put(item_l, amount);
            break :blk amount;
        };
    }

    print("{d}\n", .{sum});
}