day(09): factor out the ‹find_next›

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

src/bin/day09.rs

@@ -6,6 +6,23 @@ type Output2 = Output1;
 struct Day09 {
     values: Vec<Vec<i32>>,
 }
+
+impl Day09 {
+    fn find_next(xs: &[i32]) -> i32 {
+        let mut ds = vec![];
+
+        let mut last_row = xs.to_owned();
+        while last_row.iter().any(|&x| x != 0) {
+            let next_row = last_row.windows(2).map(|s| s[1] - s[0]).collect_vec();
+
+            ds.push(*next_row.last().unwrap());
+            last_row = next_row;
+        }
+
+        xs.last().unwrap() + ds.iter().rev().sum::<i32>()
+    }
+}
+
 impl Solution<Output1, Output2> for Day09 {
     fn new<P: AsRef<Path>>(pathname: P) -> Self {
         let values = file_to_lines::<Vec<_>, P>(pathname)
@@ -17,42 +34,19 @@ impl Solution<Output1, Output2> for Day09 {
     }
 
     fn part_1(&mut self) -> Output1 {
-        self.values
+        self.values.iter().map(|xs| Self::find_next(xs)).sum()
-            .iter()
-            .map(|xs| {
-                let mut ds = vec![];
-
-                let mut last_row = xs.clone();
-                while last_row.iter().any(|&x| x != 0) {
-                    let next_row = last_row.windows(2).map(|s| s[1] - s[0]).collect_vec();
-
-                    ds.push(*next_row.last().unwrap());
-                    last_row = next_row;
-                }
-
-                xs.last().unwrap() + ds.iter().rev().sum::<i32>()
-            })
-            .sum()
     }
 
     fn part_2(&mut self) -> Output2 {
         self.values
             .iter()
             .map(|xs| {
-                let mut ds = vec![];
+                let mut ys = xs.clone();
+                ys.reverse();
 
-                let mut last_row = xs.clone();
+                ys
-                last_row.reverse();
-
-                while last_row.iter().any(|&x| x != 0) {
-                    let next_row = last_row.windows(2).map(|s| s[1] - s[0]).collect_vec();
-
-                    ds.push(*next_row.last().unwrap());
-                    last_row = next_row;
-                }
-
-                xs.first().unwrap() + ds.iter().rev().sum::<i32>()
             })
+            .map(|xs| Self::find_next(&xs))
             .sum()
     }
 }