1 files changed, 149 insertions, 0 deletions
diff --git a/2023/src/bin/day_3.rs b/2023/src/bin/day_3.rs
new file mode 100644
index 0000000..06e1300
--- /dev/null
+++ b/2023/src/bin/day_3.rs
@@ -0,0 +1,149 @@
+use nom::{
+    branch::alt,
+    bytes::complete::tag,
+    character::complete::{digit1, line_ending, none_of},
+    combinator::{map, map_res},
+    multi::{many1, separated_list1},
+    IResult,
+};
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_3.txt")?;
+    let parsed = PartInventory::parser(&input).unwrap().1;
+    dbg!(&parsed.part_number_sum());
+    dbg!(&parsed.gear_ratio_sum());
+
+    Ok(())
+}
+
+#[derive(Debug)]
+struct PartInventory {
+    parts: Vec<Part>,
+    symbols: Vec<Symbol>,
+}
+
+#[derive(Debug)]
+struct Part {
+    number: u32,
+    symbols: Vec<char>,
+    y: usize,
+    min_x: usize,
+    max_x: usize,
+}
+
+#[derive(Debug, Clone)]
+struct Symbol {
+    symbol: char,
+    parts: Vec<u32>,
+    x: usize,
+    y: usize,
+}
+
+#[derive(Debug)]
+enum LexToken {
+    Space(usize),
+    Part(usize, u32),
+    Symbol(char),
+}
+
+impl PartInventory {
+    fn parser(input: &str) -> IResult<&str, Self> {
+        map(LexToken::parser, |tokens| {
+            let mut parts = Vec::new();
+            let mut symbols = Vec::new();
+
+            for (y, row) in tokens.iter().enumerate() {
+                let mut x = 0;
+                for token in row {
+                    match token {
+                        LexToken::Space(_) => {}
+                        LexToken::Part(len, number) => parts.push(Part {
+                            number: *number,
+                            symbols: Vec::new(),
+                            y,
+                            min_x: x,
+                            max_x: x + len - 1,
+                        }),
+                        LexToken::Symbol(symbol) => symbols.push(Symbol {
+                            symbol: *symbol,
+                            parts: Vec::new(),
+                            y,
+                            x,
+                        }),
+                    }
+                    x += token.len();
+                }
+            }
+
+            for part in &mut parts {
+                part.symbols = symbols
+                    .iter()
+                    .filter(|symbol| part.touches(symbol))
+                    .map(|symbol| symbol.symbol)
+                    .collect();
+            }
+
+            for symbol in &mut symbols {
+                symbol.parts = parts
+                    .iter()
+                    .filter(|part| part.touches(symbol))
+                    .map(|part| part.number)
+                    .collect();
+            }
+
+            PartInventory { parts, symbols }
+        })(input)
+    }
+
+    fn part_number_sum(&self) -> u32 {
+        self.parts
+            .iter()
+            .filter(|part| part.symbols.len() > 0)
+            .map(|part| part.number)
+            .sum()
+    }
+
+    fn gear_ratio_sum(&self) -> u32 {
+        self.symbols
+            .iter()
+            .filter(|symbol| symbol.symbol == '*' && symbol.parts.len() == 2)
+            .map(|symbol| symbol.parts[0] * symbol.parts[1])
+            .sum()
+    }
+}
+
+impl LexToken {
+    fn parser(input: &str) -> IResult<&str, Vec<Vec<Self>>> {
+        separated_list1(
+            line_ending,
+            many1(alt((
+                map(many1(tag(".")), |dots| LexToken::Space(dots.len())),
+                map_res(digit1, |num_s: &str| {
+                    num_s
+                        .parse()
+                        .map(|num_i| LexToken::Part(num_s.len(), num_i))
+                }),
+                map(none_of("\n"), |s| LexToken::Symbol(s)),
+            ))),
+        )(input)
+    }
+
+    fn len(&self) -> usize {
+        match self {
+            Self::Space(len) => *len,
+            Self::Part(len, _) => *len,
+            Self::Symbol(_) => 1,
+        }
+    }
+}
+
+impl Part {
+    fn touches(&self, symbol: &Symbol) -> bool {
+        let part = self;
+        symbol.x >= part.min_x.saturating_sub(1)
+            && symbol.x <= part.max_x.saturating_add(1)
+            && symbol.y >= part.y.saturating_sub(1)
+            && symbol.y <= part.y.saturating_add(1)
+    }
+}