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#[derive(Clone, Copy, Debug, Eq, PartialEq)] | |
enum Token { | |
Number(i64), | |
Add, | |
Mul, | |
OParen, | |
CParen, | |
} | |
use Token::*; | |
#[aoc_generator(day18)] | |
fn input_generator(input: &str) -> Vec<Vec<Token>> { | |
input.lines().map(parse_expr).collect() | |
} | |
fn parse_expr(expr: &str) -> Vec<Token> { | |
let mut tokens = vec![]; | |
let mut index = 0; | |
while index < expr.len() { | |
match expr.as_bytes()[index] { | |
b' ' => (), | |
b'+' => tokens.push(Add), | |
b'*' => tokens.push(Mul), | |
b'(' => tokens.push(OParen), | |
b')' => tokens.push(CParen), | |
_ => tokens.push(Number(parse_number(expr, &mut index))), | |
} | |
index += 1; | |
} | |
tokens | |
} | |
fn parse_number(input: &str, index: &mut usize) -> i64 { | |
let first = *index; | |
while *index + 1 < input.len() && (b'0'..=b'9').contains(&input.as_bytes()[*index + 1]) { | |
*index += 1; | |
} | |
unsafe { | |
std::str::from_utf8_unchecked(&input.as_bytes()[first..=*index]) | |
.parse() | |
.unwrap() | |
} | |
} | |
#[aoc(day18, part1)] | |
fn part1(exprs: &[Vec<Token>]) -> i64 { | |
exprs.iter().map(|t| eval(&*t)).sum() | |
} | |
#[aoc(day18, part2)] | |
fn part2(exprs: &[Vec<Token>]) -> i64 { | |
exprs.iter().map(|t| eval2(&*t)).sum() | |
} | |
fn eval(tokens: &[Token]) -> i64 { | |
let mut stack = vec![]; | |
for &t in tokens { | |
if t == CParen { | |
let v = stack.pop().unwrap(); | |
stack.pop(); | |
stack.push(v); | |
} else { | |
stack.push(t); | |
} | |
if stack.len() >= 3 { | |
match stack[stack.len() - 3..stack.len()] { | |
[Number(a), Add, Number(b)] => { | |
stack.truncate(stack.len() - 3); | |
stack.push(Number(a + b)) | |
} | |
[Number(a), Mul, Number(b)] => { | |
stack.truncate(stack.len() - 3); | |
stack.push(Number(a * b)) | |
} | |
_ => (), | |
} | |
} | |
} | |
if let Number(a) = stack.pop().unwrap() { | |
a | |
} else { | |
unreachable!() | |
} | |
} | |
fn eval2(tokens: &[Token]) -> i64 { | |
let mut stack = vec![]; | |
for &t in tokens { | |
if t == CParen { | |
while stack[stack.len() - 2] != OParen { | |
match stack[stack.len() - 3..stack.len()] { | |
[Number(a), Mul, Number(b)] => { | |
stack.truncate(stack.len() - 3); | |
stack.push(Number(a * b)); | |
} | |
_ => unreachable!(), | |
} | |
} | |
let v = stack.pop().unwrap(); | |
stack.pop(); | |
stack.push(v); | |
} else { | |
stack.push(t); | |
} | |
if stack.len() >= 3 { | |
match stack[stack.len() - 3..stack.len()] { | |
[Number(a), Add, Number(b)] => { | |
stack.truncate(stack.len() - 3); | |
stack.push(Number(a + b)) | |
} | |
_ => (), | |
} | |
} | |
} | |
stack | |
.into_iter() | |
.step_by(2) | |
.map(|t| match t { | |
Number(a) => a, | |
_ => unreachable!(), | |
}) | |
.product() | |
} |
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