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use std::fs;
use std::collections::HashMap;
enum Oper<'a> {
IncReg,
DecReg,
CpyReg(&'a str),
CpyLit(isize),
JnzReg(&'a str, isize),
JnzLit(isize, isize),
}
fn parse(lines: Vec<&str>) -> Vec<(Oper, &str)> {
// We emit tuples of type `(Oper, &str)', where the second field
// is the destination register. Storing the destination this way,
// instead of inside the `Oper' enum, helps keep `execute()' DRY.
let mut insts = Vec::new();
for line in lines {
let words: Vec<&str> = line.split_ascii_whitespace().collect();
if words[0] == "inc" {
// words[1] is register name
insts.push((Oper::IncReg, words[1]));
} else if words[0] == "dec" {
// words[1] is register name
insts.push((Oper::DecReg, words[1]));
} else if words[0] == "cpy" {
// words[1] is source, can be literal number or register name
// words[2] is destination register name
if words[1].chars().all(|c| c.is_ascii_digit() || c == '-') { // yes I know
let val = words[1].parse().unwrap();
insts.push((Oper::CpyLit(val), words[2]));
} else {
insts.push((Oper::CpyReg(words[1]), words[2]));
}
} else if words[0] == "jnz" {
// words[1] is value, can be literal number or register name
// words[2] is offset to jump by if branch is taken
let off = words[2].parse().unwrap();
if words[1].chars().all(|c| c.is_ascii_digit() || c == '-') { // I know
let val = words[1].parse().unwrap();
insts.push((Oper::JnzLit(val, off), "_"));
} else {
insts.push((Oper::JnzReg(words[1], off), "_"));
}
}
}
insts
}
fn execute(insts: &Vec<(Oper, &str)>, init: Vec<(&str, isize)>) -> isize {
// `init' contains initial register values
let mut state: HashMap<&str, isize> = init.into_iter().collect();
let mut ip = 0; // instruction pointer
while ip < insts.len() {
// Get destination register now, because we'll mess with `ip' later
let dst = insts[ip].1;
// Too early for mutable borrow of `state', so write to `tmp' instead
let mut tmp = state.get(dst).copied().unwrap_or(0);
match insts[ip].0 {
Oper::IncReg => {
tmp += 1;
},
Oper::DecReg => {
tmp -= 1;
},
Oper::CpyLit(val) => {
tmp = val;
},
Oper::CpyReg(src) => {
let val = state.get(&src).copied().unwrap_or(0);
tmp = val;
},
Oper::JnzLit(val, off) => {
if val != 0 {
// Subtract 1 to compensate for `ip += 1;' below
ip = ((ip as isize) + off - 1) as usize;
}
},
Oper::JnzReg(src, off) => {
let val = state.get(&src).copied().unwrap_or(0);
if val != 0 {
// Subtract 1 to compensate for `ip += 1;' below
ip = ((ip as isize) + off - 1) as usize;
}
},
};
// "_" is a dummy destination register used by the "jnz" instructions
if dst != "_" {
*state.entry(dst).or_insert(0) = tmp;
}
ip += 1;
}
state.get("a").copied().unwrap()
}
fn main() {
// Read assembly from input text file and parse it
let input = fs::read_to_string("input.txt").unwrap();
let lines = input.lines().collect();
let insts = parse(lines);
// Part 1 gives 318117 for my input
println!("Part 1 solution: {}", execute(&insts, vec![]));
// Part 2 gives 9227771 for my input
println!("Part 2 solution: {}", execute(&insts, vec![("c", 1)]));
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn part1_example1() {
let lines = vec!["cpy 41 a", "inc a", "inc a", "dec a", "jnz a 2", "dec a"];
let insts = parse(lines);
assert_eq!(execute(&insts, vec![]), 42);
}
}
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