Day 13 part 1

1 files changed, 66 insertions, 8 deletions

diff --git a/2023/src/bin/day_13.rs b/2023/src/bin/day_13.rs
index b3a610b..b2ef8aa 100644
--- a/2023/src/bin/day_13.rs
+++ b/2023/src/bin/day_13.rs
@@ -1,19 +1,77 @@
-use nom::IResult;
+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_2.txt")?;
-    let parsed = Example::parser(&input).unwrap().1;
-    dbg!(&parsed);
+    let input = fs::read_to_string("inputs/day_13.txt")?;
+    let parsed = ManyMaps::parser(&input).unwrap().1;
+    dbg!(&parsed.reflection_score_sum());
 
     Ok(())
 }
 
 #[derive(Debug)]
-struct Example;
+struct ManyMaps(Vec<Map>);
 
-impl Example {
-    fn parser(_input: &str) -> IResult<&str, Self> {
-        todo!()
+#[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) -> usize {
+        self.0.iter().map(|m| m.reflection_score()).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) -> usize {
+        reflection_i(&self.cols)
+            .or_else(|| reflection_i(&self.rows).map(|y| y * 100))
+            .expect("No reflection!")
+    }
+}
+
+fn reflection_i(rows: &[String]) -> Option<usize> {
+    for i in 1..rows.len() {
+        let mut is_reflection = true;
+        let mut d = 1;
+        while is_reflection && d <= i && d + i - 1 < rows.len() {
+            if rows[i - d] != rows[i + d - 1] {
+                is_reflection = false;
+            }
+            d += 1;
+        }
+        if is_reflection {
+            return Some(i);
+        }
     }
+    None
 }