Day 13 part 2

1 files changed, 19 insertions, 14 deletions

diff --git a/2023/src/bin/day_13.rs b/2023/src/bin/day_13.rs
index b2ef8aa..ad97602 100644
--- a/2023/src/bin/day_13.rs
+++ b/2023/src/bin/day_13.rs
@@ -10,7 +10,8 @@ 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());
+    dbg!(&parsed.reflection_score_sum(0));
+    dbg!(&parsed.reflection_score_sum(1));
 
     Ok(())
 }
@@ -32,8 +33,11 @@ impl ManyMaps {
         )(input)
     }
 
-    fn reflection_score_sum(&self) -> usize {
-        self.0.iter().map(|m| m.reflection_score()).sum()
+    fn reflection_score_sum(&self, expected_smudge_count: usize) -> usize {
+        self.0
+            .iter()
+            .map(|m| m.reflection_score(expected_smudge_count))
+            .sum()
     }
 }
 
@@ -52,23 +56,24 @@ impl Map {
         })(input)
     }
 
-    fn reflection_score(&self) -> usize {
-        reflection_i(&self.cols)
-            .or_else(|| reflection_i(&self.rows).map(|y| y * 100))
+    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]) -> Option<usize> {
+fn reflection_i(rows: &[String], expected_smudge_count: usize) -> 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;
+        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);
         }