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const std = @import("std");
const mecha = @import("mecha");
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');
if (std.mem.eql(u8, part, "1")) {
try part1(&lines, allocator);
} else {
try part2(&lines, allocator);
}
}
fn get_ordering_rules(lines: *std.mem.SplitIterator(u8, .scalar), allocator: std.mem.Allocator) !std.AutoHashMap(usize, std.ArrayList(usize)) {
var ordering_rules = std.AutoHashMap(usize, std.ArrayList(usize)).init(allocator);
errdefer ordering_rules.deinit();
const parser = mecha.combine(.{ mecha.int(usize, .{}), mecha.ascii.char('|').discard(), mecha.int(usize, .{}) });
// PAGE ORDERING RULES
while (lines.next()) |line| {
if (line.len == 0) {
break;
}
const parsed = try parser.parse(allocator, line);
if (ordering_rules.getPtr(parsed.value[0])) |value| {
try value.append(parsed.value[1]);
} else {
var list = std.ArrayList(usize).init(allocator);
errdefer list.deinit();
try list.append(parsed.value[1]);
try ordering_rules.put(parsed.value[0], list);
}
}
return ordering_rules;
}
fn part1(lines: *std.mem.SplitIterator(u8, .scalar), allocator: std.mem.Allocator) !void {
var ordering_rules = try get_ordering_rules(lines, allocator);
defer ordering_rules.deinit();
var total: usize = 0;
// UPDATES
outer: while (lines.next()) |line| {
if (line.len == 0) {
break;
}
var list = std.ArrayList(usize).init(allocator);
defer list.deinit();
var covered_numbers = std.AutoHashMap(usize, void).init(allocator);
defer covered_numbers.deinit();
var page_numbers = std.mem.splitScalar(u8, line, ',');
while (page_numbers.next()) |page_number| {
const number = try std.fmt.parseInt(usize, page_number, 10);
try covered_numbers.put(number, {});
try list.append(number);
const next = ordering_rules.get(number) orelse continue;
for (next.items) |n| {
if (covered_numbers.contains(n)) {
continue :outer;
}
}
}
total += list.items[list.items.len / 2];
}
print("{d}\n", .{total});
}
//-----------------------PART 2----------------------------
fn reorder(list: *std.ArrayList(usize), ordering_rules: *std.AutoHashMap(usize, std.ArrayList(usize)), allocator: std.mem.Allocator) !bool {
var covered_numbers = std.AutoHashMap(usize, usize).init(allocator);
defer covered_numbers.deinit();
for (list.items, 0..) |number, i| {
try covered_numbers.put(number, i);
const next = ordering_rules.get(number) orelse continue;
for (next.items) |n| {
if (covered_numbers.get(n)) |index| {
list.items[i] = n;
list.items[index] = number;
return false;
}
}
}
return true;
}
fn part2(lines: *std.mem.SplitIterator(u8, .scalar), allocator: std.mem.Allocator) !void {
var ordering_rules = try get_ordering_rules(lines, allocator);
defer ordering_rules.deinit();
var total: usize = 0;
// UPDATES
while (lines.next()) |line| {
if (line.len == 0) {
break;
}
var list = std.ArrayList(usize).init(allocator);
defer list.deinit();
var page_numbers = std.mem.splitScalar(u8, line, ',');
while (page_numbers.next()) |page_number| {
const number = try std.fmt.parseInt(usize, page_number, 10);
try list.append(number);
}
var incorrect = false;
while (!try reorder(&list, &ordering_rules, allocator)) {
incorrect = true;
}
if (incorrect) {
total += list.items[list.items.len / 2];
}
}
print("{d}\n", .{total});
}
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