2020: day18: part 2
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426ea00636
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@ -18,6 +18,7 @@ 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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writeln!(res, "part 2: {}", part2(INPUT)?)?;
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Ok(res)
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}
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@ -25,7 +26,22 @@ pub fn run() -> Result<String> {
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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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.map(|line| {
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terminated(expr, eof)(line)
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.map_err(|_| anyhow!("couldn't parse expr"))
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.map(|(_, e)| e.eval())
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})
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.sum()
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}
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fn part2(input: &str) -> Result<u64> {
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input
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.lines()
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.map(|line| {
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terminated(plus_priority, eof)(line)
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.map_err(|_| anyhow!("couldn't parse expr"))
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.map(|(_, e)| e.eval())
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})
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.sum()
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}
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@ -73,28 +89,57 @@ fn operator_expr(input: &str) -> IResult<&str, Expr> {
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)(i)
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}
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fn plus(input: &str) -> IResult<&str, Expr> {
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let (i, first_term) = term_plus_priority(input)?;
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fold_many0(
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pair(
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delimited(char(' '), char('+'), char(' ')),
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term_plus_priority,
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),
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first_term,
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|acc, (_, val)| Expr::Op(Box::new(acc), Operator::Addition, Box::new(val)),
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)(i)
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}
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fn mul(input: &str) -> IResult<&str, Expr> {
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let (i, first_factor) = plus(input)?;
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fold_many0(
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pair(delimited(char(' '), char('*'), char(' ')), plus),
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first_factor,
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|acc, (_, val)| Expr::Op(Box::new(acc), Operator::Multiplication, 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 paren(input: &str) -> IResult<&str, Expr> {
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delimited(char('('), expr, char(')'))(input)
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}
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fn paren_plus_priority(input: &str) -> IResult<&str, Expr> {
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delimited(char('('), plus_priority, char(')'))(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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alt((paren, num))(input)
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}
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fn term_plus_priority(input: &str) -> IResult<&str, Expr> {
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alt((paren_plus_priority, 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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fn plus_priority(input: &str) -> IResult<&str, Expr> {
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alt((mul, term_plus_priority))(input)
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}
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#[cfg(test)]
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@ -112,9 +157,36 @@ mod tests {
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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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for (exp, expected) in tests {
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let (_, exp) = terminated(expr, eof)(exp).unwrap();
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assert_eq!(exp.eval(), *expected);
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}
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}
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#[test]
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fn part1_real() {
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assert_eq!(part1(INPUT).unwrap(), 800602729153);
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}
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#[test]
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fn part2_provided() {
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let tests = &[
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("1 + 2 * 3 + 4 * 5 + 6", 231),
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("1 + (2 * 3) + (4 * (5 + 6))", 51),
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("2 * 3 + (4 * 5)", 46),
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("5 + (8 * 3 + 9 + 3 * 4 * 3)", 1445),
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("5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))", 669060),
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("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2", 23340),
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];
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for (exp, expected) in tests {
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let (_, exp) = terminated(plus_priority, eof)(exp).unwrap();
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assert_eq!(exp.eval(), *expected);
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}
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}
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#[test]
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fn part2_real() {
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assert_eq!(part2(INPUT).unwrap(), 92173009047076);
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}
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}
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