Completed day 18

day18/src/main.rs

@@ -0,0 +1,156 @@
+extern crate nom;
+
+use anyhow::Result;
+use nom::{
+    branch::alt,
+    bytes::complete::tag,
+    character::complete::char,
+    character::complete::{digit1 as digit, space0 as space},
+    combinator::map_res,
+    multi::fold_many0,
+    sequence::{delimited, pair},
+    IResult,
+};
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::str::FromStr;
+use std::time::Instant;
+
+const INPUT: &str = "input/input.txt";
+
+// From: https://github.com/Geal/nom/blob/master/tests/arithmetic.rs
+fn flat_parens(i: &str) -> IResult<&str, i64> {
+    delimited(space, delimited(tag("("), flat_expr, tag(")")), space)(i)
+}
+
+fn flat_factor(i: &str) -> IResult<&str, i64> {
+    alt((
+        map_res(delimited(space, digit, space), FromStr::from_str),
+        flat_parens,
+    ))(i)
+}
+
+fn flat_expr(i: &str) -> IResult<&str, i64> {
+    let (i, init) = flat_factor(i)?;
+
+    fold_many0(
+        pair(alt((char('+'), char('*'))), flat_factor),
+        init,
+        |acc, (op, val): (char, i64)| {
+            if op == '+' {
+                acc + val
+            } else if op == '*' {
+                acc * val
+            } else {
+                acc
+            }
+        },
+    )(i)
+}
+
+fn precedent_parens(i: &str) -> IResult<&str, i64> {
+    delimited(space, delimited(tag("("), precedent_expr, tag(")")), space)(i)
+}
+
+fn precedent_factor(i: &str) -> IResult<&str, i64> {
+    alt((
+        map_res(delimited(space, digit, space), FromStr::from_str),
+        precedent_parens,
+    ))(i)
+}
+
+fn sum(i: &str) -> IResult<&str, i64> {
+    let (i, init) = precedent_factor(i)?;
+
+    fold_many0(
+        pair(char('+'), precedent_factor),
+        init,
+        |acc, (op, val): (char, i64)| {
+            if op == '+' {
+                acc + val
+            } else {
+                acc
+            }
+        },
+    )(i)
+}
+
+fn precedent_expr(i: &str) -> IResult<&str, i64> {
+    let (i, init) = sum(i)?;
+
+    fold_many0(pair(char('*'), sum), init, |acc, (op, val): (char, i64)| {
+        if op == '*' {
+            acc * val
+        } else {
+            acc
+        }
+    })(i)
+}
+
+fn solve_part1(input_path: &str) -> Result<i64> {
+    let file = File::open(input_path)?;
+    let reader = BufReader::new(file);
+    Ok(reader
+        .lines()
+        .map(|line| flat_expr(&line.unwrap()).unwrap().1)
+        .sum::<i64>())
+}
+
+fn solve_part2(input_path: &str) -> Result<i64> {
+    let file = File::open(input_path)?;
+    let reader = BufReader::new(file);
+    Ok(reader
+        .lines()
+        .map(|line| precedent_expr(&line.unwrap()).unwrap().1)
+        .sum::<i64>())
+}
+
+fn main() {
+    let mut now = Instant::now();
+    println!("Part 1: {}", solve_part1(INPUT).unwrap());
+    println!("(elapsed: {:?})", now.elapsed());
+    now = Instant::now();
+    println!("");
+    println!("Part 2: {}", solve_part2(INPUT).unwrap());
+    println!("(elapsed: {:?})", now.elapsed());
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn solves_part1() {
+        assert_eq!(flat_expr("1 + 2 * 3 + 4 * 5 + 6"), Ok(("", 71)));
+        assert_eq!(flat_expr("1 + (2 * 3) + (4 * (5 + 6))"), Ok(("", 51)));
+        assert_eq!(flat_expr("2 * 3 + (4 * 5)"), Ok(("", 26)));
+        assert_eq!(flat_expr("5 + (8 * 3 + 9 + 3 * 4 * 3)"), Ok(("", 437)));
+        assert_eq!(
+            flat_expr("5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))"),
+            Ok(("", 12240))
+        );
+        assert_eq!(
+            flat_expr("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2"),
+            Ok(("", 13632))
+        );
+    }
+
+    #[test]
+    fn solves_part2() {
+        assert_eq!(precedent_expr("1 + 2 * 3 + 4 * 5 + 6"), Ok(("", 231)));
+        assert_eq!(precedent_expr("1 + (2 * 3) + (4 * (5 + 6))"), Ok(("", 51)));
+        assert_eq!(precedent_expr("2 * 3 + (4 * 5)"), Ok(("", 46)));
+        assert_eq!(
+            precedent_expr("5 + (8 * 3 + 9 + 3 * 4 * 3)"),
+            Ok(("", 1445))
+        );
+        assert_eq!(
+            precedent_expr("5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))"),
+            Ok(("", 669060))
+        );
+        assert_eq!(
+            precedent_expr("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2"),
+            Ok(("", 23340))
+        );
+    }
+}