day 13 part 2

2023/day-13/src/part2.rs

@@ -1,19 +1,150 @@
+use std::iter::from_fn;
+
 use color_eyre::Result;
+use itertools::Itertools;
+
+#[derive(Debug, PartialEq, Eq)]
+enum Fold {
+    Horizontal(usize),
+    Vertical(usize),
+}
+
+fn detect_fold(input: &str) -> Option<Fold> {
+    detect_vertical_fold(input).or(detect_horizontal_fold(input))
+}
+
+fn detect_vertical_fold(input: &str) -> Option<Fold> {
+    let mut columns_iter_collection = input.lines().map(|line| line.chars()).collect::<Vec<_>>();
+    let columns = from_fn(move || {
+        let mut items = Vec::new();
+        for iter in &mut columns_iter_collection {
+            match iter.next() {
+                Some(item) => items.push(item),
+                None => return None,
+            }
+        }
+        Some(items)
+    })
+    .collect::<Vec<_>>();
+    let result = columns
+        .iter()
+        .enumerate()
+        .tuple_windows()
+        .filter(|((_, line_a), (_, line_b))| {
+            line_a == line_b
+                || line_a
+                    .iter()
+                    .zip(line_b.iter())
+                    .filter(|(a, b)| a != b)
+                    .count()
+                    <= 1
+        })
+        .find_map(|((index_a, _), (index_b, _))| {
+            let lines_a = (&columns[0..=index_a]).iter().rev();
+            let lines_b = (&columns[index_b..]).iter();
+            (lines_a
+                .flatten()
+                .zip(lines_b.flatten())
+                .filter(|(a, b)| a != b)
+                .count()
+                == 1)
+                .then_some(index_a + 1)
+        });
+    result.map(|num| Fold::Vertical(num))
+}
+
+fn detect_horizontal_fold(input: &str) -> Option<Fold> {
+    let lines = input.lines().collect::<Vec<_>>();
+    let result = input
+        .lines()
+        .enumerate()
+        .tuple_windows()
+        .filter(|((_, line_a), (_, line_b))| {
+            line_a == line_b
+                || line_a
+                    .chars()
+                    .zip(line_b.chars())
+                    .filter(|(a, b)| a != b)
+                    .count()
+                    <= 1
+        })
+        .find_map(|((index_a, _), (index_b, _))| {
+            let lines_a = (&lines[0..=index_a]).iter().map(|line| line.chars()).rev();
+            let lines_b = (&lines[index_b..]).iter().map(|line| line.chars());
+            (lines_a
+                .flatten()
+                .zip(lines_b.flatten())
+                .filter(|(a, b)| a != b)
+                .count()
+                == 1)
+                .then_some(index_a + 1)
+        });
+    result.map(|num| Fold::Horizontal(num))
+}
 
 pub fn process(input: &str) -> Result<usize> {
-    todo!("day xx - part 2");
-    Ok(0)
+    let (horizontal, vertical) =
+        input
+            .split("\n\n")
+            .flat_map(detect_fold)
+            .fold((0, 0), |mut acc, item| match item {
+                Fold::Horizontal(num) => {
+                    acc.0 += 100 * num;
+                    acc
+                }
+                Fold::Vertical(num) => {
+                    acc.1 += num;
+                    acc
+                }
+            });
+    Ok(horizontal + vertical)
 }
 
 #[cfg(test)]
 mod tests {
+
     use super::*;
 
     #[test]
     fn test_process() -> Result<()> {
-        let input = "";
-        todo!("haven't built test yet");
-        assert_eq!(0, process(input)?);
+        let input = "#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#";
+        assert_eq!(400, process(input)?);
+        Ok(())
+    }
+
+    #[test]
+    fn test_horizontal() -> Result<()> {
+        let input = "#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#";
+        assert_eq!(Some(Fold::Horizontal(1)), detect_fold(input));
+
+        let input = "#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.";
+        assert_eq!(Some(Fold::Horizontal(3)), detect_fold(input));
         Ok(())
     }
 }