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use crate::input::Input;
type Word = i32;
#[derive(Copy, Clone)]
pub enum Instruction {
Acc(Word),
Jmp(Word),
Nop(Word),
}
pub struct Computer {
pub instructions: Vec<Instruction>,
pub accumulator: Word,
pub instruction_pointer: Word,
}
impl Computer {
pub fn parse(program_text: &str) -> Result<Self, String> {
let instructions = program_text
.lines()
.enumerate()
.map(|(line_idx, line)| {
if line.len() < 6 {
return Err(format!(
"Line {}: Too short line ({})",
line_idx + 1,
line.len()
));
}
let argument = line[4..]
.parse::<Word>()
.map_err(|e| format!("Line {}: Cannot parse argument - {}", line_idx + 1, e))?;
Ok(match &line[0..3] {
"acc" => Instruction::Acc(argument),
"jmp" => Instruction::Jmp(argument),
"nop" => Instruction::Nop(argument),
_ => {
return Err(format!(
"Line {}: Invalid line not starting with acc/jmp/nop",
line_idx + 1
));
}
})
})
.collect::<Result<Vec<_>, _>>()?;
Ok(Self {
instructions,
accumulator: 0,
instruction_pointer: 0,
})
}
pub fn execute_instruction(&mut self) -> Result<(), String> {
if self.has_exited() {}
match self.instructions.get(self.instruction_pointer as usize) {
Some(Instruction::Acc(parameter)) => {
self.accumulator += parameter;
}
Some(Instruction::Jmp(parameter)) => {
self.instruction_pointer += parameter;
return Ok(());
}
Some(Instruction::Nop(_)) => {}
None => {
return Err("Cannot executed an exited program".to_string());
}
};
self.instruction_pointer += 1;
Ok(())
}
pub fn has_exited(&self) -> bool {
self.instruction_pointer < 0 || self.instruction_pointer >= self.instructions.len() as Word
}
}
struct ComputerChecker {
executed_instructions: Vec<bool>,
}
impl ComputerChecker {
fn new(computer: &Computer) -> Self {
Self {
executed_instructions: vec![false; computer.instructions.len()],
}
}
fn check_if_exits(&mut self, computer: &mut Computer) -> Result<bool, String> {
self.executed_instructions
.iter_mut()
.for_each(|v| *v = false);
while !computer.has_exited()
&& !self.executed_instructions[computer.instruction_pointer as usize]
{
self.executed_instructions[computer.instruction_pointer as usize] = true;
computer.execute_instruction()?;
}
Ok(computer.has_exited())
}
}
pub fn solve(input: &Input) -> Result<Word, String> {
let mut computer = Computer::parse(input.text)?;
let mut computer_checker = ComputerChecker::new(&computer);
computer_checker.check_if_exits(&mut computer)?;
if input.is_part_one() {
Ok(computer.accumulator)
} else {
let executed_instructions_without_patch = computer_checker.executed_instructions.clone();
for i in executed_instructions_without_patch
.iter()
.enumerate()
.filter_map(|(idx, &executed)| if executed { Some(idx) } else { None })
{
let instruction = computer.instructions[i];
match instruction {
Instruction::Jmp(parameter) | Instruction::Nop(parameter) => {
computer.instructions[i] = if matches!(instruction, Instruction::Jmp(_)) {
Instruction::Nop(parameter)
} else {
Instruction::Jmp(parameter)
};
if computer_checker.check_if_exits(&mut computer)? {
return Ok(computer.accumulator);
}
computer.instruction_pointer = 0;
computer.accumulator = 0;
computer.instructions[i] = instruction;
}
_ => {
continue;
}
}
}
Err("No instruction modification causes program to exit".to_string())
}
}
#[test]
pub fn tests() {
use crate::input::{test_part_one, test_part_two};
let example = "nop +0
acc +1
jmp +4
acc +3
jmp -3
acc -99
acc +1
jmp -4
acc +6";
test_part_one!(example => 5);
test_part_two!(example => 8);
let real_input = include_str!("day08_input.txt");
test_part_one!(real_input => 1684);
test_part_two!(real_input => 2188);
}