126 lines
4.7 KiB
Zig
126 lines
4.7 KiB
Zig
const std = @import("std");
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const example = @embedFile("example");
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const input = @embedFile("input");
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pub fn main() anyerror!void {
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var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
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defer arena.deinit();
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const allocator = arena.allocator();
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try std.testing.expectEqual(try solve(example, allocator), 10605);
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const result = try solve(input, allocator);
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try std.io.getStdOut().writer().print("{}\n", .{result});
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}
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const Operation = struct {
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first: ?u64,
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operand: u8,
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second: ?u64,
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fn init(line: []const u8, allocator: std.mem.Allocator) !*Operation {
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var o = try allocator.create(Operation);
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var it = std.mem.tokenize(u8, line, " ");
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_ = it.next() orelse unreachable; // Operation:
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_ = it.next() orelse unreachable; // new
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_ = it.next() orelse unreachable; // =
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o.first = std.fmt.parseInt(u64, it.next() orelse unreachable, 10) catch null;
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const tmp = it.next() orelse unreachable;
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o.operand = tmp[0];
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o.second = std.fmt.parseInt(u64, it.next() orelse unreachable, 10) catch null;
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return o;
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}
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fn run(o: Operation, v: u64) u64 {
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const first = if (o.first) |f| f else v;
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const second = if (o.second) |f| f else v;
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switch (o.operand) {
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'+' => return first + second,
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'-' => return first - second,
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'*' => return first * second,
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'/' => return first / second,
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else => unreachable,
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}
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}
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};
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const Monkey = struct {
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inspections: u64,
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items: std.ArrayList(u64),
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operation: *Operation,
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divisible: u64, // divisible by
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testTrue: u64,
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testFalse: u64,
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fn init(it: *std.mem.TokenIterator(u8), allocator: std.mem.Allocator) !*Monkey {
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var m = try allocator.create(Monkey);
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m.inspections = 0;
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m.items = std.ArrayList(u64).init(allocator);
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var items = std.mem.tokenize(u8, it.next() orelse unreachable, " ,");
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_ = items.next() orelse unreachable; // starting
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_ = items.next() orelse unreachable; // items:
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while (items.next()) |item| {
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try m.items.append(std.fmt.parseInt(u64, item, 10) catch unreachable);
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}
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m.operation = try Operation.init(it.next() orelse unreachable, allocator);
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var divisible = std.mem.tokenize(u8, it.next() orelse unreachable, " ");
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_ = divisible.next() orelse unreachable; // test:
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_ = divisible.next() orelse unreachable; // divisible
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_ = divisible.next() orelse unreachable; // by
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m.divisible = std.fmt.parseInt(u64, divisible.next() orelse unreachable, 10) catch unreachable;
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var testTrue = std.mem.tokenize(u8, it.next() orelse unreachable, " ");
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_ = testTrue.next() orelse unreachable; // if
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_ = testTrue.next() orelse unreachable; // true:
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_ = testTrue.next() orelse unreachable; // throw
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_ = testTrue.next() orelse unreachable; // to
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_ = testTrue.next() orelse unreachable; // monkey
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m.testTrue = std.fmt.parseInt(u64, testTrue.next() orelse unreachable, 10) catch unreachable;
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var testFalse = std.mem.tokenize(u8, it.next() orelse unreachable, " ");
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_ = testFalse.next() orelse unreachable; // if
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_ = testFalse.next() orelse unreachable; // true:
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_ = testFalse.next() orelse unreachable; // throw
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_ = testFalse.next() orelse unreachable; // to
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_ = testFalse.next() orelse unreachable; // monkey
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m.testFalse = std.fmt.parseInt(u64, testFalse.next() orelse unreachable, 10) catch unreachable;
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return m;
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}
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fn step(m: *Monkey, monkeys: []*Monkey) !void {
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m.inspections += m.items.items.len;
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for (m.items.items) |item| {
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const v = m.operation.run(item) / 3;
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if (@mod(v, m.divisible) == 0) {
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try monkeys[m.testTrue].items.append(v);
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} else {
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try monkeys[m.testFalse].items.append(v);
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}
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}
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m.items.items.len = 0;
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}
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};
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fn solve(puzzle: []const u8, allocator: std.mem.Allocator) !u64 {
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var it = std.mem.tokenize(u8, puzzle, "\n");
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var monkeys = std.ArrayList(*Monkey).init(allocator);
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// process input
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while (it.next()) |_| {
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try monkeys.append(try Monkey.init(&it, allocator));
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}
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// run 20 rounds
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var rounds: usize = 0;
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while (rounds < 20) : (rounds += 1) {
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for (monkeys.items) |m| {
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try m.step(monkeys.items);
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}
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}
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// find answer
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var m1: u64 = 0;
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var m2: u64 = 0;
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for (monkeys.items) |m| {
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if (m.inspections > m1) {
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m2 = m1;
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m1 = m.inspections;
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continue;
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}
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if (m.inspections > m2) {
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m2 = m.inspections;
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}
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}
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return m1 * m2;
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}
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