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use advent_lib::prelude::*;
use std::convert::TryFrom;
use std::collections::BTreeSet;
#[derive(Clone, Debug)]
enum Operation {
Accumulator(isize),
Jump(isize),
NoOp(isize),
}
#[derive(Clone, Debug)]
struct MachineState {
accumulator: isize,
program_counter: usize,
}
impl MachineState {
fn new() -> MachineState {
MachineState {
accumulator: 0,
program_counter: 0,
}
}
}
fn main() -> Result<()> {
let mut args = std::env::args();
if args.len() != 2 {
eprintln!("Usage: advent input");
}
let _ = args.next();
let filename = args.next().unwrap();
let input = advent_lib::read_lines_file(&filename)?;
let program = parse_program(&input)?;
find_first_loop(&program);
find_patch_to_terminate(&program);
Ok(())
}
fn parse_program(input: &Vec<String>) -> Result<Vec<Operation>> {
let mut program: Vec<Operation> = Vec::new();
for line in input {
let mut words = Vec::new();
for word in line.split(' ') {
words.push(word);
}
let operand = words[1].parse::<isize>()?;
match words[0] {
"acc" => program.push(Operation::Accumulator(operand)),
"jmp" => program.push(Operation::Jump(operand)),
"nop" => program.push(Operation::NoOp(operand)),
_ => panic!()
}
}
Ok(program)
}
fn simulate_one(program: &Vec<Operation>, state: &MachineState) -> MachineState {
let mut new_state = state.clone();
match program[new_state.program_counter] {
Operation::Accumulator(operand) => {
new_state.accumulator += operand;
new_state.program_counter += 1;
},
Operation::Jump(operand) => {
new_state.program_counter = usize::try_from(
isize::try_from(new_state.program_counter).unwrap()
+ operand).unwrap();
},
Operation::NoOp(_) => {
new_state.program_counter += 1;
},
}
new_state
}
fn find_first_loop(program: &Vec<Operation>) -> () {
let mut visited_lines: BTreeSet<usize> = BTreeSet::new();
let mut state = MachineState::new();
loop {
if visited_lines.contains(&state.program_counter) {
println!("{}", state.accumulator);
break;
}
visited_lines.insert(state.program_counter);
state = simulate_one(&program, &state);
}
}
fn find_patch_to_terminate(program: &Vec<Operation>) -> () {
for i in 0..program.len() {
let mut patched_program = program.clone();
match patched_program[i] {
Operation::Accumulator(_) => {
continue;
},
Operation::Jump(operand) => {
patched_program[i] = Operation::NoOp(operand);
},
Operation::NoOp(operand) => {
patched_program[i] = Operation::Jump(operand);
},
}
let mut visited_lines: BTreeSet<usize> = BTreeSet::new();
let mut state = MachineState::new();
let mut normal_exit = false;
loop {
if visited_lines.contains(&state.program_counter) {
break;
}
if state.program_counter == patched_program.len() {
println!("normal exit {}", state.accumulator);
normal_exit = true;
break;
}
visited_lines.insert(state.program_counter);
state = simulate_one(&patched_program, &state);
}
if normal_exit {
break;
}
}
}
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