1 files changed, 82 insertions, 0 deletions
diff --git a/2023/src/bin/day_13.rs b/2023/src/bin/day_13.rs
new file mode 100644
index 0000000..ad97602
--- /dev/null
+++ b/2023/src/bin/day_13.rs
@@ -0,0 +1,82 @@
+use nom::{
+    character::complete::{line_ending, one_of},
+    combinator::map,
+    multi::{many1, separated_list1},
+    sequence::pair,
+    IResult,
+};
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_13.txt")?;
+    let parsed = ManyMaps::parser(&input).unwrap().1;
+    dbg!(&parsed.reflection_score_sum(0));
+    dbg!(&parsed.reflection_score_sum(1));
+
+    Ok(())
+}
+
+#[derive(Debug)]
+struct ManyMaps(Vec<Map>);
+
+#[derive(Debug)]
+struct Map {
+    rows: Vec<String>,
+    cols: Vec<String>,
+}
+
+impl ManyMaps {
+    fn parser(input: &str) -> IResult<&str, Self> {
+        map(
+            separated_list1(pair(line_ending, line_ending), Map::parser),
+            ManyMaps,
+        )(input)
+    }
+
+    fn reflection_score_sum(&self, expected_smudge_count: usize) -> usize {
+        self.0
+            .iter()
+            .map(|m| m.reflection_score(expected_smudge_count))
+            .sum()
+    }
+}
+
+impl Map {
+    fn parser(input: &str) -> IResult<&str, Self> {
+        map(separated_list1(line_ending, many1(one_of(".#"))), |rows| {
+            Map {
+                rows: rows
+                    .iter()
+                    .map(|char_array| char_array.iter().collect::<String>())
+                    .collect(),
+                cols: (0..rows[0].len())
+                    .map(|i| rows.iter().map(|row| row[i]).collect::<String>())
+                    .collect(),
+            }
+        })(input)
+    }
+
+    fn reflection_score(&self, expected_smudge_count: usize) -> usize {
+        reflection_i(&self.cols, expected_smudge_count)
+            .or_else(|| reflection_i(&self.rows, expected_smudge_count).map(|y| y * 100))
+            .expect("No reflection!")
+    }
+}
+
+fn reflection_i(rows: &[String], expected_smudge_count: usize) -> Option<usize> {
+    for i in 1..rows.len() {
+        let mut smudge_count = 0;
+        for d in 1..=(i.min(rows.len() - i)) {
+            smudge_count += rows[i - d]
+                .chars()
+                .zip(rows[i + d - 1].chars())
+                .filter(|(a, b)| a != b)
+                .count();
+        }
+        let is_reflection = smudge_count == expected_smudge_count;
+        if is_reflection {
+            return Some(i);
+        }
+    }
+    None
+}