diff --git a/src/bin/day13.rs b/src/bin/day13.rs
index 3bba81c..8cae9b3 100644
--- a/src/bin/day13.rs
+++ b/src/bin/day13.rs
@@ -19,17 +19,13 @@ impl From<&[String]> for Pattern {
 }
 
 impl Pattern {
-    fn check_vertically(&self, allowed_error: usize) -> Option<i32> {
-        (0..self.map[0].len() - 1)
-            .find(|&x| {
-                let d = min(x + 1, self.map[0].len() - x - 1);
-
-                iproduct!(0..self.map.len(), (1..=d))
-                    .filter(|&(y, dx)| self.map[y][x + 1 - dx] != self.map[y][x + dx])
-                    .count()
-                    == allowed_error
-            })
-            .map(|x| (x + 1) as i32)
+    fn transpose(&self) -> Pattern {
+        let (m, n) = (self.map.len(), self.map[0].len());
+        Pattern {
+            map: (0..n)
+                .map(|x| (0..m).map(|y| self.map[y][x]).collect_vec())
+                .collect_vec(),
+        }
     }
 
     fn check_horizontally(&self, allowed_error: usize) -> Option<i32> {
@@ -46,7 +42,7 @@ impl Pattern {
     }
 
     fn score(&self, allowed_error: usize) -> i32 {
-        if let Some(s) = self.check_vertically(allowed_error) {
+        if let Some(s) = self.transpose().check_horizontally(allowed_error) {
             s
         } else if let Some(s) = self.check_horizontally(allowed_error) {
             100 * s