121 lines
2.8 KiB
Rust
121 lines
2.8 KiB
Rust
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use std::fmt::Write;
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use anyhow::{anyhow, Result};
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use nom::{
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branch::alt,
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bytes::complete::take_while1,
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character::complete::{char, one_of},
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combinator::{eof, map_res},
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multi::fold_many0,
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sequence::{delimited, pair, terminated},
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IResult, Parser,
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};
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const INPUT: &str = include_str!("../input/day18.txt");
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pub fn run() -> Result<String> {
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let mut res = String::with_capacity(128);
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writeln!(res, "part 1: {}", part1(INPUT)?)?;
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Ok(res)
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}
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fn part1(input: &str) -> Result<u64> {
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input
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.lines()
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.map(|line| line.parse::<Expr>().map(|e| e.eval()))
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.sum()
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}
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#[derive(Debug, Clone, Copy)]
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enum Operator {
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Addition,
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Multiplication,
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}
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#[derive(Debug, Clone)]
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enum Expr {
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Num(u64),
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Op(Box<Expr>, Operator, Box<Expr>),
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}
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impl Expr {
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fn eval(&self) -> u64 {
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match self {
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Self::Num(val) => *val,
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Self::Op(lhs, op, rhs) => match op {
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Operator::Addition => lhs.eval() + rhs.eval(),
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Operator::Multiplication => lhs.eval() * rhs.eval(),
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},
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}
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}
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}
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fn operator(input: &str) -> IResult<&str, Operator> {
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one_of("+*")
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.map(|op| match op {
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'+' => Operator::Addition,
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'*' => Operator::Multiplication,
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_ => unreachable!(),
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})
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.parse(input)
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}
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fn operator_expr(input: &str) -> IResult<&str, Expr> {
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let (i, first_term) = term(input)?;
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fold_many0(
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pair(delimited(char(' '), operator, char(' ')), term),
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first_term,
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|acc, (op, val)| Expr::Op(Box::new(acc), op, Box::new(val)),
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)(i)
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}
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fn num(input: &str) -> IResult<&str, Expr> {
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map_res(take_while1(|c: char| c.is_digit(10)), |res: &str| {
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res.parse().map(Expr::Num)
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})(input)
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}
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fn term(input: &str) -> IResult<&str, Expr> {
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alt((delimited(char('('), expr, char(')')), num))(input)
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}
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fn expr(input: &str) -> IResult<&str, Expr> {
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alt((operator_expr, term))(input)
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}
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impl std::str::FromStr for Expr {
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type Err = anyhow::Error;
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fn from_str(s: &str) -> Result<Self> {
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let (_, res) = terminated(expr, eof)(s).map_err(|_| anyhow!("couldn't parse expr"))?;
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Ok(res)
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn part1_provided() {
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let tests = &[
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("1 + 2 * 3 + 4 * 5 + 6", 71),
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("1 + (2 * 3) + (4 * (5 + 6))", 51),
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("2 * 3 + (4 * 5)", 26),
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("5 + (8 * 3 + 9 + 3 * 4 * 3)", 437),
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("5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))", 12240),
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("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2", 13632),
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];
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for (expr, expected) in tests {
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let expr: Expr = expr.parse().unwrap();
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assert_eq!(expr.eval(), *expected);
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}
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}
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}
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