1 files changed, 156 insertions, 0 deletions
diff --git a/day18.cc b/day18.cc
new file mode 100644
index 0000000..8a73064
--- /dev/null
+++ b/day18.cc
@@ -0,0 +1,156 @@
+#include <iostream>
+#include <string>
+#include <algorithm>
+#include <variant>
+#include <vector>
+#include <deque>
+#include <memory>
+
+using namespace std;
+
+int part;
+int p1 = 0;
+int p2 = 0;
+
+struct cpu;
+
+struct insn {
+	virtual void run(cpu &) = 0;
+	virtual bool stalled(cpu &) { return false; }
+};
+
+struct cpu {
+	int64_t reg[256];
+	const vector<unique_ptr<insn>> &insns;
+	vector<unique_ptr<insn>>::const_iterator ip;
+	deque<uint64_t> &sndq, &rcvq;
+	int id;
+
+	cpu(const vector<unique_ptr<insn>> &insns,
+	    deque<uint64_t> &sq, deque<uint64_t> &rq, int id=0) :
+		reg{0}, insns{insns}, ip{cbegin(insns)}, sndq{sq}, rcvq{rq},
+		id{id}
+	{
+		reg[(uint8_t)'p'] = id;
+	}
+
+	void step() { (*ip++)->run(*this); }
+	bool done() { return ip == cend(insns); }
+	bool stalled() { return (*ip)->stalled(*this); }
+};
+
+struct arg {
+	virtual long operator()(cpu &) = 0;
+};
+
+struct const_arg : arg {
+	long l;
+	const_arg(long l) : l{l} {}
+	long operator()(cpu &) { return l; }
+};
+
+struct reg_arg : arg {
+	uint8_t r;
+	reg_arg(uint8_t r) : r{r} {}
+	long operator()(cpu &c) { return c.reg[r]; }
+};
+
+unique_ptr<arg>
+parse(string s) {
+	if (islower(s[0]))
+		return make_unique<reg_arg>(uint8_t(s[0]));
+	else
+		return make_unique<const_arg>(stol(s));
+}
+
+struct binop : public insn {
+public:
+	uint8_t r;
+	unique_ptr<arg> a;
+	binop(string &s) : r(s[4]), a{parse(&s[6])} {};
+};
+
+struct opset : public binop { using binop::binop;
+	void run(cpu &c) { c.reg[r] = (*a)(c); }
+};
+struct opadd : public binop { using binop::binop;
+	void run(cpu &c) { c.reg[r] += (*a)(c); }
+};
+struct opmul : public binop { using binop::binop;
+	void run(cpu &c) { c.reg[r] *= (*a)(c); }
+};
+struct opmod : public binop { using binop::binop;
+	void run(cpu &c) { c.reg[r] %= (*a)(c); }
+};
+struct opjgz : public insn {
+	unique_ptr<arg> a1, a2;
+	opjgz(string &s) : a1{parse(&s[4])}, a2{parse(&s[6])} {}
+	void run(cpu &c) { if ((*a1)(c) > 0) advance(c.ip, (*a2)(c) - 1); }
+};
+struct opsnd : public insn {
+	unique_ptr<arg> a;
+	opsnd(string &s) : a{parse(&s[4])} {}
+	void run(cpu &c) { 
+		if (part == 1) {
+			p1 = (*a)(c);
+		} else {
+			if (c.id == 1)
+				p2++;
+			c.sndq.push_back((*a)(c));
+		}
+	}
+};
+struct oprcv : public insn {
+	uint8_t r;
+	oprcv(string &s) : r(s[4]) {}
+	void run(cpu &c) {
+		if (part == 2) {
+			if (empty(c.rcvq)) {
+				--c.ip;
+			} else {
+				c.reg[r] = c.rcvq.front();
+				c.rcvq.pop_front();
+			}
+		}
+	}
+	bool stalled(cpu &c) { return part == 1 ? c.reg[r] > 0 : empty(c.rcvq); }
+};
+
+int
+main() {
+	string line;
+	vector<unique_ptr<insn>> code;
+
+	while (getline(cin, line)) {
+		auto is_op = [&](string p){
+			return equal(begin(p), end(p), begin(line));
+		};
+
+		insn* op;
+		if      (is_op("set")) op = new opset{line};
+		else if (is_op("add")) op = new opadd{line};
+		else if (is_op("mul")) op = new opmul{line};
+		else if (is_op("mod")) op = new opmod{line};
+		else if (is_op("jgz")) op = new opjgz{line};
+		else if (is_op("snd")) op = new opsnd{line};
+		else if (is_op("rcv")) op = new oprcv{line};
+		code.emplace_back(op);
+	}
+
+	part = 1;
+
+	deque<uint64_t> _;
+	for (cpu c{code, _, _}; !c.done() && !c.stalled(); c.step())
+		;
+
+	part = 2;
+
+	deque<uint64_t> q01, q10;
+	for (cpu c0{code, q01, q10, 0},
+		 c1{code, q10, q01, 1};
+	     !c0.done() && !c1.done() && !(c0.stalled() && c1.stalled());
+	     c0.step(), c1.step())
+		;
+
+	cout << p1 << endl << p2 << endl;	// 3423 7493
+}