2021: day10: part 1

aoc2021/src/day10.rs

@@ -0,0 +1,125 @@
+use std::fmt::Write;
+
+use anyhow::{bail, Result};
+
+const INPUT: &str = include_str!("../input/day10.txt");
+
+pub fn run() -> Result<String> {
+    let mut res = String::with_capacity(128);
+
+    writeln!(res, "part 1: {}", part1(INPUT)?)?;
+
+    Ok(res)
+}
+
+fn part1(input: &str) -> Result<u64> {
+    let lines = input
+        .lines()
+        .map(str::parse::<Line>)
+        .collect::<Result<Vec<_>>>()?;
+
+    Ok(lines.iter().map(Line::corrupt_score).sum())
+}
+
+enum SymbolState {
+    Open(Symbol),
+    Close(Symbol),
+}
+
+impl TryFrom<char> for SymbolState {
+    type Error = anyhow::Error;
+
+    fn try_from(value: char) -> Result<Self> {
+        match value {
+            '(' | '[' | '{' | '<' => Ok(SymbolState::Open(value.try_into().unwrap())),
+            ')' | ']' | '}' | '>' => Ok(SymbolState::Close(value.try_into().unwrap())),
+            _ => bail!("invalid char for symbol"),
+        }
+    }
+}
+
+#[derive(PartialEq, Eq)]
+enum Symbol {
+    Parenthesis,  // ()
+    Bracket,      // []
+    Brace,        // {}
+    AngleBracket, // <>
+}
+
+impl Symbol {
+    fn score(&self) -> u64 {
+        match self {
+            Symbol::Parenthesis => 3,
+            Symbol::Bracket => 57,
+            Symbol::Brace => 1197,
+            Symbol::AngleBracket => 25137,
+        }
+    }
+}
+
+impl TryFrom<char> for Symbol {
+    type Error = anyhow::Error;
+
+    fn try_from(value: char) -> Result<Self> {
+        match value {
+            '(' | ')' => Ok(Symbol::Parenthesis),
+            '[' | ']' => Ok(Symbol::Bracket),
+            '{' | '}' => Ok(Symbol::Brace),
+            '<' | '>' => Ok(Symbol::AngleBracket),
+            _ => bail!("invalid char for symbol"),
+        }
+    }
+}
+
+struct Line {
+    symbols: Vec<SymbolState>,
+}
+
+impl Line {
+    fn corrupt_score(&self) -> u64 {
+        let mut stack = Vec::new();
+
+        for state in &self.symbols {
+            match state {
+                SymbolState::Open(symbol) => stack.push(symbol),
+                SymbolState::Close(symbol) => match stack.pop() {
+                    Some(other_symbol) if symbol == other_symbol => continue,
+                    _ => return symbol.score(),
+                },
+            }
+        }
+
+        0
+    }
+}
+
+impl std::str::FromStr for Line {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self> {
+        Ok(Line {
+            symbols: s
+                .trim()
+                .chars()
+                .map(TryFrom::try_from)
+                .collect::<Result<Vec<_>>>()?,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PROVIDED: &str = include_str!("../input/day10_provided.txt");
+
+    #[test]
+    fn part1_provided() {
+        assert_eq!(part1(PROVIDED).unwrap(), 26397);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 394647);
+    }
+}

aoc2021/src/lib.rs

@@ -9,3 +9,4 @@ pub mod day06;
 pub mod day07;
 pub mod day08;
 pub mod day09;
+pub mod day10;

aoc2021/src/main.rs

@@ -11,6 +11,7 @@ use aoc2021::day06;
 use aoc2021::day07;
 use aoc2021::day08;
 use aoc2021::day09;
+use aoc2021::day10;
 
 fn main() -> Result<()> {
     let days: &[DayFunc] = &[
@@ -23,6 +24,7 @@ fn main() -> Result<()> {
         day07::run,
         day08::run,
         day09::run,
+        day10::run,
     ];
 
     aoc::run(days)