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use std::io::{self, Read};
use std::iter;
#[derive(Clone, Copy)]
enum Operand {
Register(u8),
Immediate(i32),
}
impl<'a> From<&'a str> for Operand {
fn from(s: &'a str) -> Self {
match s {
"a" => Operand::Register(0),
"b" => Operand::Register(1),
"c" => Operand::Register(2),
"d" => Operand::Register(3),
_ => Operand::Immediate(s.parse().unwrap()),
}
}
}
#[derive(Clone, Copy)]
enum Operation {
Cpy(Operand, Operand),
Inc(Operand),
Dec(Operand),
Jnz(Operand, Operand),
Tgl(Operand),
Out(Operand),
}
impl<'a> From<&'a str> for Operation {
fn from(s: &'a str) -> Self {
let mut iter = s.split_whitespace();
match (iter.next().unwrap(), iter.next().unwrap()) {
("cpy", a) => Operation::Cpy(Operand::from(a), Operand::from(iter.next().unwrap())),
("inc", a) => Operation::Inc(Operand::from(a)),
("dec", a) => Operation::Dec(Operand::from(a)),
("jnz", a) => Operation::Jnz(Operand::from(a), Operand::from(iter.next().unwrap())),
("tgl", a) => Operation::Tgl(Operand::from(a)),
("out", a) => Operation::Out(Operand::from(a)),
_ => panic!("invalid instruction {}", s),
}
}
}
impl Operation {
fn toggle(self) -> Self {
match self {
Operation::Inc(a) => Operation::Dec(a),
Operation::Dec(a) | Operation::Tgl(a) => Operation::Inc(a),
Operation::Jnz(a, b) => Operation::Cpy(a, b),
Operation::Cpy(a, b) => Operation::Jnz(a, b),
_ => unimplemented!(),
}
}
}
#[derive(Default)]
struct Vm {
registers: [i32; 4],
operations: Vec<Operation>,
index: i32,
output: Vec<i32>,
}
impl<'a> From<&'a str> for Vm {
fn from(s: &'a str) -> Self {
let mut vm = Self::default();
for line in s.lines() {
vm.operations.push(Operation::from(line));
}
vm
}
}
impl Vm {
fn step(&mut self) -> bool {
match self.operations[self.index as usize] {
Operation::Cpy(Operand::Immediate(imm), Operand::Register(reg)) => {
self.registers[reg as usize] = imm;
self.index += 1;
},
Operation::Cpy(Operand::Register(src), Operand::Register(dest)) => {
self.registers[dest as usize] = self.registers[src as usize];
self.index += 1;
},
Operation::Inc(Operand::Register(reg)) => {
self.registers[reg as usize] += 1;
self.index += 1;
},
Operation::Dec(Operand::Register(reg)) => {
self.registers[reg as usize] -= 1;
self.index += 1;
},
Operation::Jnz(Operand::Immediate(cond), Operand::Immediate(jump)) => {
if cond != 0 {
self.index += jump;
} else {
self.index += 1;
}
},
Operation::Jnz(Operand::Register(reg), Operand::Immediate(jump)) => {
if self.registers[reg as usize] != 0 {
self.index += jump;
} else {
self.index += 1;
}
},
Operation::Jnz(Operand::Immediate(cond), Operand::Register(reg)) => {
if cond != 0 {
self.index += self.registers[reg as usize];
} else {
self.index += 1;
}
},
Operation::Tgl(Operand::Register(reg)) => {
let index = self.index + self.registers[reg as usize];
if let Some(operation) = self.operations.get_mut(index as usize) {
*operation = operation.toggle();
}
self.index += 1;
},
Operation::Out(Operand::Immediate(imm)) => {
self.output.push(imm);
self.index += 1;
},
Operation::Out(Operand::Register(reg)) => {
self.output.push(self.registers[reg as usize]);
self.index += 1;
},
_ => {
self.index += 1;
},
}
(self.index as usize) < self.operations.len()
}
}
fn solve(input: &str) -> i32 {
for i in 0.. {
let mut vm = Vm::from(input);
vm.registers[0] = i;
while vm.output.len() < 50 {
assert!(vm.step());
}
let target = iter::once(0).chain(iter::once(1)).cycle().take(50);
if vm.output.into_iter().eq(target) {
return i;
}
}
unreachable!()
}
fn main() {
let mut input = String::new();
io::stdin().read_to_string(&mut input).unwrap();
println!("Part 1: {}", solve(&input));
}
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