day13: problem 2 solution

13/src/main.rs

@@ -43,51 +43,75 @@ impl Pattern {
     }
 
     fn find_horizontal_reflection(&self) -> Option<usize> {
-        println!("looking for horiz: {:?}", (1..self.height() - 1).collect::<Vec<_>>());
         (1..self.height()).find(|idx| self.is_horizontal_reflection(*idx))
     }
 
     fn is_horizontal_reflection(&self, idx: usize) -> bool {
         let row_pairs = std::cmp::min(idx, self.height() - idx);
-        (0..row_pairs).all(|offset| {
-            println!(
-                "{}: [{} == {}] {:?} == {:?}",
-                idx,
-                idx - offset - 1,
-                idx + offset,
-                self.mirrors[idx - offset - 1],
-                self.mirrors[idx + offset]
-            );
-            self.mirrors[idx - offset - 1] == self.mirrors[idx + offset]
-        })
+        (0..row_pairs).all(|offset| self.mirrors[idx - offset - 1] == self.mirrors[idx + offset])
     }
 
     fn find_vertical_reflection(&self) -> Option<usize> {
-        println!("looking for vert: {:?}", (1..self.width() - 1).collect::<Vec<_>>());
-        (1..self.width() ).find(|idx| self.is_vertical_reflection(*idx))
+        (1..self.width()).find(|idx| self.is_vertical_reflection(*idx))
     }
 
     fn is_vertical_reflection(&self, idx: usize) -> bool {
         let col_pairs = std::cmp::min(idx, self.width() - idx);
-        (0..col_pairs).all(|offset| {
-            println!(
-                "{}: [{} == {}] {:?} == {:?}",
-                idx,
-                idx - offset - 1,
-                idx + offset,
-                self.col(idx - offset - 1),
-                self.col(idx + offset)
-            );
-            self.col(idx - offset - 1) == self.col(idx + offset)
-        })
+        (0..col_pairs).all(|offset| self.col(idx - offset - 1) == self.col(idx + offset))
+    }
+
+    fn find_smudged_horizontal_reflection(&self) -> Option<usize> {
+        (1..self.height()).find(|idx| self.is_smudged_horizontal_reflection(*idx))
+    }
+
+    fn is_smudged_horizontal_reflection(&self, idx: usize) -> bool {
+        // Same algorithm for problem 2, but count errors breaking reflection.
+        // If the count == 1 after all checks, then it is our smudge
+        let row_pairs = std::cmp::min(idx, self.height() - idx);
+        (0..row_pairs)
+            .map(|offset| {
+                self.mirrors[idx - offset - 1]
+                    .iter()
+                    .zip(self.mirrors[idx + offset].iter())
+                    .filter(|(a, b)| **a != **b)
+                    .count()
+            })
+            .sum::<usize>()
+            == 1
+    }
+
+    fn find_smudged_vertical_reflection(&self) -> Option<usize> {
+        (1..self.width()).find(|idx| self.is_smudged_vertical_reflection(*idx))
+    }
+
+    fn is_smudged_vertical_reflection(&self, idx: usize) -> bool {
+        let col_pairs = std::cmp::min(idx, self.width() - idx);
+        (0..col_pairs)
+            .map(|offset| {
+                self.col(idx - offset - 1)
+                    .iter()
+                    .zip(self.col(idx + offset).iter())
+                    .filter(|(a, b)| **a != **b)
+                    .count()
+            })
+            .sum::<usize>()
+            == 1
     }
 
     fn reflection_cost(&self) -> u64 {
         if let Some(refl) = self.find_horizontal_reflection() {
-            println!("horizontal found at {}", refl);
             100 * refl as u64
         } else if let Some(refl) = self.find_vertical_reflection() {
-            println!("vertical found at {}", refl);
+            refl as u64
+        } else {
+            panic!("no reflection");
+        }
+    }
+
+    fn smudged_reflection_cost(&self) -> u64 {
+        if let Some(refl) = self.find_smudged_horizontal_reflection() {
+            100 * refl as u64
+        } else if let Some(refl) = self.find_smudged_vertical_reflection() {
             refl as u64
         } else {
             panic!("no reflection");
@@ -125,13 +149,19 @@ fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
     patterns
         .patterns
         .iter()
-        .map(|pat| { println!("{:?}", pat); pat.reflection_cost() })
+        .map(|pat| pat.reflection_cost())
         .sum()
 }
 
 // PROBLEM 2 solution
 fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
-    0
+    let patterns = Patterns::from(input);
+
+    patterns
+        .patterns
+        .iter()
+        .map(|pat| pat.smudged_reflection_cost())
+        .sum()
 }
 
 #[cfg(test)]
@@ -175,9 +205,23 @@ mod tests {
         assert_eq!(problem1(c.lines()), 405);
     }
 
+    #[test]
+    fn problem2_find_horizontal() {
+        let c = Cursor::new(EXAMPLE);
+        let patterns = Patterns::from(c.lines());
+        assert_eq!(
+            patterns.patterns[0].find_smudged_horizontal_reflection(),
+            Some(3)
+        );
+        assert_eq!(
+            patterns.patterns[1].find_smudged_horizontal_reflection(),
+            Some(1)
+        );
+    }
+
     #[test]
     fn problem2_example() {
         let c = Cursor::new(EXAMPLE);
-        assert_eq!(problem2(c.lines()), 0);
+        assert_eq!(problem2(c.lines()), 400);
     }
 }