2022-11 in zig

2022/11-monkey-in-the-middle/second.zig

@@ -0,0 +1,129 @@
+const std = @import("std");
+
+const example = @embedFile("example");
+const input = @embedFile("input");
+
+pub fn main() anyerror!void {
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const allocator = arena.allocator();
+
+    try std.testing.expectEqual(try solve(example, allocator), 2713310158);
+    const result = try solve(input, allocator);
+    try std.io.getStdOut().writer().print("{}\n", .{result});
+}
+
+const Operation = struct {
+    first: ?u64,
+    operand: u8,
+    second: ?u64,
+    fn init(line: []const u8, allocator: std.mem.Allocator) !*Operation {
+        var o = try allocator.create(Operation);
+        var it = std.mem.tokenize(u8, line, " ");
+        _ = it.next() orelse unreachable; // Operation:
+        _ = it.next() orelse unreachable; // new
+        _ = it.next() orelse unreachable; // =
+        o.first = std.fmt.parseInt(u64, it.next() orelse unreachable, 10) catch null;
+        const tmp = it.next() orelse unreachable;
+        o.operand = tmp[0];
+        o.second = std.fmt.parseInt(u64, it.next() orelse unreachable, 10) catch null;
+        return o;
+    }
+    fn run(o: Operation, v: u64) u64 {
+        const first = if (o.first) |f| f else v;
+        const second = if (o.second) |f| f else v;
+        switch (o.operand) {
+            '+' => return first + second,
+            '-' => return first - second,
+            '*' => return first * second,
+            '/' => return first / second,
+            else => unreachable,
+        }
+    }
+};
+
+const Monkey = struct {
+    inspections: u64,
+    items: std.ArrayList(u64),
+    operation: *Operation,
+    divisible: u64, // divisible by
+    testTrue: u64,
+    testFalse: u64,
+    fn init(it: *std.mem.TokenIterator(u8), allocator: std.mem.Allocator) !*Monkey {
+        var m = try allocator.create(Monkey);
+        m.inspections = 0;
+        m.items = std.ArrayList(u64).init(allocator);
+        var items = std.mem.tokenize(u8, it.next() orelse unreachable, " ,");
+        _ = items.next() orelse unreachable; // starting
+        _ = items.next() orelse unreachable; // items:
+        while (items.next()) |item| {
+            try m.items.append(std.fmt.parseInt(u64, item, 10) catch unreachable);
+        }
+        m.operation = try Operation.init(it.next() orelse unreachable, allocator);
+        var divisible = std.mem.tokenize(u8, it.next() orelse unreachable, " ");
+        _ = divisible.next() orelse unreachable; // test:
+        _ = divisible.next() orelse unreachable; // divisible
+        _ = divisible.next() orelse unreachable; // by
+        m.divisible = std.fmt.parseInt(u64, divisible.next() orelse unreachable, 10) catch unreachable;
+        var testTrue = std.mem.tokenize(u8, it.next() orelse unreachable, " ");
+        _ = testTrue.next() orelse unreachable; // if
+        _ = testTrue.next() orelse unreachable; // true:
+        _ = testTrue.next() orelse unreachable; // throw
+        _ = testTrue.next() orelse unreachable; // to
+        _ = testTrue.next() orelse unreachable; // monkey
+        m.testTrue = std.fmt.parseInt(u64, testTrue.next() orelse unreachable, 10) catch unreachable;
+        var testFalse = std.mem.tokenize(u8, it.next() orelse unreachable, " ");
+        _ = testFalse.next() orelse unreachable; // if
+        _ = testFalse.next() orelse unreachable; // true:
+        _ = testFalse.next() orelse unreachable; // throw
+        _ = testFalse.next() orelse unreachable; // to
+        _ = testFalse.next() orelse unreachable; // monkey
+        m.testFalse = std.fmt.parseInt(u64, testFalse.next() orelse unreachable, 10) catch unreachable;
+        return m;
+    }
+    fn step(m: *Monkey, monkeys: []*Monkey, bigModulo: u64) !void {
+        m.inspections += m.items.items.len;
+        for (m.items.items) |item| {
+            const v = @mod(m.operation.run(item), bigModulo);
+            if (@mod(v, m.divisible) == 0) {
+                try monkeys[m.testTrue].items.append(v);
+            } else {
+                try monkeys[m.testFalse].items.append(v);
+            }
+        }
+        m.items.items.len = 0;
+    }
+};
+
+fn solve(puzzle: []const u8, allocator: std.mem.Allocator) !u64 {
+    var it = std.mem.tokenize(u8, puzzle, "\n");
+    var monkeys = std.ArrayList(*Monkey).init(allocator);
+    var bigModulo: u64 = 1;
+    // process input
+    while (it.next()) |_| {
+        var m = try monkeys.addOne();
+        m.* = try Monkey.init(&it, allocator);
+        bigModulo *= m.*.divisible;
+    }
+    // run 10k rounds
+    var rounds: usize = 0;
+    while (rounds < 10000) : (rounds += 1) {
+        for (monkeys.items) |m| {
+            try m.step(monkeys.items, bigModulo);
+        }
+    }
+    // find answer
+    var m1: u64 = 0;
+    var m2: u64 = 0;
+    for (monkeys.items) |m| {
+        if (m.inspections > m1) {
+            m2 = m1;
+            m1 = m.inspections;
+            continue;
+        }
+        if (m.inspections > m2) {
+            m2 = m.inspections;
+        }
+    }
+    return m1 * m2;
+}