Day 13 Complete 0 -> Initially implemented with a hashmap however this was not viable for the second part so followed AxlLinds solution to adapt it for the second part of the challenge.

src/input/day13_test1

@@ -0,0 +1,15 @@
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#

src/input/day13_test2

@@ -0,0 +1,15 @@
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#

src/main.rs

@@ -20,7 +20,7 @@ async fn main() -> Result<(), Box<dyn Error>> {
         Box::new(day10::Day10 {}),
         Box::new(day11::Day11 {}),
         Box::new(day12::Day12 {}),
-        // Box::new(day13::Day13 {}),
+        Box::new(day13::Day13 {}),
         // Box::new(day14::Day14 {}),
         // Box::new(day15::Day15 {}),
         // Box::new(day16::Day16 {}),

src/solutions/day13.rs

@@ -1,3 +1,5 @@
+use itertools::Itertools;
+
 use super::Solution;
 
 pub struct Day13 {}
@@ -5,16 +7,28 @@ pub struct Day13 {}
 impl Solution for Day13 {
     fn part1(
         &self,
-        _input: &mut Vec<String>,
+        input: &mut Vec<String>,
     ) -> Result<Box<dyn std::fmt::Display + Sync>, Box<dyn std::error::Error>> {
-        Ok(Box::new("Ready"))
+        let binding = input.clone().iter().join("\n");
+        let grids = binding
+            .split("\n\n")
+            .map(|s| s.split("\n").map(|l| l.as_bytes()).collect::<Vec<_>>())
+            .collect::<Vec<_>>();
+
+        Ok(Box::new(self.solve(&grids, 0)))
     }
 
     fn part2(
         &self,
-        _input: &mut Vec<String>,
+        input: &mut Vec<String>,
     ) -> Result<Box<dyn std::fmt::Display + Sync>, Box<dyn std::error::Error>> {
-        Ok(Box::new("Ready"))
+        let binding = input.clone().iter().join("\n");
+        let grids = binding
+            .split("\n\n")
+            .map(|s| s.split("\n").map(|l| l.as_bytes()).collect::<Vec<_>>())
+            .collect::<Vec<_>>();
+
+        Ok(Box::new(self.solve(&grids, 1)))
     }
 
     fn get_day(&self) -> u8 {
@@ -22,7 +36,53 @@ impl Solution for Day13 {
     }
 }
 
-impl Day13 {}
+impl Day13 {
+    // Finds the index of the column where the reflection is located
+    fn find_col_reflection(&self, grid: &[&[u8]], limit: usize) -> Option<usize> {
+        (0..grid[0].len() - 1).find(|&c| {
+            let incorrect = (0..=c.min(grid[0].len() - c - 2))
+                .map(|dc| {
+                    let a = c - dc;
+                    let b = c + 1 + dc;
+                    (0..grid.len())
+                        .filter(|&r| grid[r][a] != grid[r][b])
+                        .count()
+                })
+                .sum::<usize>();
+            incorrect == limit
+        })
+    }
+
+    // Finds the index of the row where the reflection is located
+    fn find_row_reflection(&self, grid: &[&[u8]], limit: usize) -> Option<usize> {
+        (0..grid.len() - 1).find(|&r| {
+            let incorrect = (0..=r.min(grid.len() - r - 2))
+                .map(|dr| {
+                    let a = r - dr;
+                    let b = r + 1 + dr;
+                    (0..grid[0].len())
+                        .filter(|&c| grid[a][c] != grid[b][c])
+                        .count()
+                })
+                .sum::<usize>();
+            incorrect == limit
+        })
+    }
+
+    // Gets the given score for a reflection
+    // where limit is the index of the reflection you want to find in each image
+    fn solve(&self, grids: &[Vec<&[u8]>], limit: usize) -> usize {
+        grids
+            .iter()
+            .map(|grid| {
+                self.find_row_reflection(grid, limit)
+                    .map(|r| (r + 1) * 100)
+                    .or_else(|| self.find_col_reflection(grid, limit).map(|c| c + 1))
+                    .unwrap()
+            })
+            .sum()
+    }
+}
 
 /// Test from puzzle input
 #[cfg(test)]
@@ -44,7 +104,7 @@ mod test {
             .unwrap()
             .to_string();
 
-        assert_eq!(answer, "Ready");
+        assert_eq!(answer, "405");
     }
 
     #[test]
@@ -61,6 +121,6 @@ mod test {
             .unwrap()
             .to_string();
 
-        assert_eq!(answer, "Ready");
+        assert_eq!(answer, "400");
     }
 }