day(12): refactor ‹unfold› and test it

Signed-off-by: Matej Focko <mfocko@redhat.com>

src/bin/day12.rs

@@ -9,7 +9,7 @@ use aoc_2023::*;
 type Output1 = usize;
 type Output2 = Output1;
 
-#[derive(Debug)]
+#[derive(Debug, PartialEq, Eq)]
 struct Row {
     map: VecDeque<char>,
     damaged: VecDeque<usize>,
@@ -118,9 +118,12 @@ impl Row {
 
     fn unfold(&self) -> Row {
         Row::new(
-            vec![self.map.iter().collect::<String>(); 5]
+            self.map
-                .join("?")
+                .iter()
-                .chars()
+                .cloned()
+                .chain(['?'])
+                .cycle()
+                .take(5 * (self.map.len() + 1) - 1)
                 .collect_vec(),
             self.damaged
                 .iter()
@@ -166,6 +169,29 @@ test_sample!(day_12, Day12, 21, 525152);
 mod day_12_extended {
     use super::*;
 
+    #[test]
+    fn unfold_1() {
+        let row = Row::new(".#".chars().collect_vec(), vec![1]);
+        assert_eq!(
+            row.unfold(),
+            Row::new(".#?.#?.#?.#?.#".chars().collect_vec(), vec![1, 1, 1, 1, 1])
+        );
+    }
+
+    #[test]
+    fn unfold_2() {
+        let row = Row::new("???.###".chars().collect_vec(), vec![1, 1, 3]);
+        assert_eq!(
+            row.unfold(),
+            Row::new(
+                "???.###????.###????.###????.###????.###"
+                    .chars()
+                    .collect_vec(),
+                vec![1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3]
+            )
+        );
+    }
+
     #[test]
     fn arrangements_1() {
         let mut row = Row::new("???.###".chars().collect_vec(), vec![1, 1, 3]);