day 12 part 2

src/day12.rs

@@ -1,5 +1,7 @@
 use std::{collections::HashSet, fs::read_to_string};
 
+use itertools::Itertools;
+
 use crate::utils::grid::{Coord, Grid};
 
 pub fn day_main() {
@@ -44,12 +46,117 @@ fn part1(input: &str) -> RiddleResult {
     result
 }
 
-fn part2(_input: &str) -> RiddleResult {
-    0
+fn part2(input: &str) -> RiddleResult {
+    let garden = Grid::parse(input);
+    let mut processed: HashSet<Coord> = HashSet::new();
+    let mut result = 0;
+    for (p, c) in garden.entries() {
+        if processed.contains(&p) {
+            continue;
+        }
+        let mut area = 0;
+        let mut further = vec![p];
+        let mut group = HashSet::new();
+        while let Some(current) = further.pop() {
+            if processed.contains(&current) {
+                continue;
+            }
+            group.insert(current);
+            area += 1;
+            for next in NEIGHBORS.iter().map(|d| (current.0 + d.0, current.1 + d.1)) {
+                let next_c = garden.get(next);
+                if next_c.is_none() || next_c.unwrap() != c {
+                } else {
+                    further.push(next);
+                }
+            }
+            processed.insert(current);
+        }
+        result += area * sides(group);
+    }
+    result
+}
+
+fn sides(group: HashSet<(i64, i64)>) -> RiddleResult {
+    let x_range = group.iter().min_by_key(|it| it.0).unwrap().0
+        ..=group.iter().max_by_key(|it| it.0).unwrap().0;
+    let y_range = group.iter().min_by_key(|it| it.1).unwrap().1
+        ..=group.iter().max_by_key(|it| it.1).unwrap().1;
+    let mut result = 0;
+    for x in x_range {
+        // 1 for the ending of the last group, +1 for each time a line "stops", e.g. between the current point and next there is a gap
+        let points = group
+            .iter()
+            .filter(|p| p.0 == x)
+            .filter(|p| !group.contains(&(p.0 - 1, p.1)))
+            .sorted_by_key(|p| p.1)
+            .collect_vec();
+        if points.is_empty() {
+        } else {
+            let count = points
+                .into_iter()
+                .tuple_windows()
+                .filter(|(a, b)| a.1 + 1 != b.1)
+                .count();
+            result += 1 + count;
+        }
+        let points = group
+            .iter()
+            .filter(|p| p.0 == x)
+            .filter(|p| !group.contains(&(p.0 + 1, p.1)))
+            .sorted_by_key(|p| p.1)
+            .collect_vec();
+        if points.is_empty() {
+        } else {
+            let count = points
+                .into_iter()
+                .tuple_windows()
+                .filter(|(a, b)| a.1 + 1 != b.1)
+                .count();
+            result += 1 + count;
+        }
+    }
+    for y in y_range {
+        let points = group
+            .iter()
+            .filter(|p| p.1 == y)
+            .filter(|p| !group.contains(&(p.0, p.1 - 1)))
+            .sorted_by_key(|p| p.0)
+            .collect_vec();
+        if points.is_empty() {
+        } else {
+            let count = points
+                .into_iter()
+                .tuple_windows()
+                .filter(|(a, b)| a.0 + 1 != b.0)
+                .count();
+            result += 1 + count;
+        }
+        let points = group
+            .iter()
+            .filter(|p| p.1 == y)
+            .filter(|p| !group.contains(&(p.0, p.1 + 1)))
+            .sorted_by_key(|p| p.0)
+            .collect_vec();
+        if points.is_empty() {
+        } else {
+            let count = points
+                .into_iter()
+                .tuple_windows()
+                .filter(|(a, b)| a.0 + 1 != b.0)
+                .count();
+            result += 1 + count;
+        }
+    }
+    result as RiddleResult
 }
 
 #[cfg(test)]
 mod test {
+    use std::collections::HashSet;
+
+    use crate::day12::sides;
+
     use super::{part1, part2};
 
     const TEST_INPUT: &str = r"AAAA
@@ -65,6 +172,18 @@ EEEC
 
     #[test]
     fn test2() {
-        assert_eq!(part2(TEST_INPUT), 0);
+        assert_eq!(part2(TEST_INPUT), 80);
+    }
+
+    #[test]
+    fn sides_one() {
+        let group = HashSet::from_iter([(3, 5)]);
+        assert_eq!(sides(group), 4);
+    }
+
+    #[test]
+    fn sides_plus() {
+        let group = HashSet::from_iter([(3, 3), (3, 4), (3, 2), (2, 3), (4, 3)]);
+        assert_eq!(sides(group), 12);
     }
 }