Solve 2023 day 9 part 2

jeffs · Dec 9, 2023 · 9a76d84 · 9a76d84
1 parent 87777d6
commit 9a76d84
Showing 5 changed files with 72 additions and 30 deletions.
diff --git a/2023/day9/src/lib.rs b/2023/day9/src/lib.rs
@@ -1 +1,3 @@
 pub mod part1;
+pub mod part2;
+mod row;
diff --git a/2023/day9/src/main.rs b/2023/day9/src/main.rs
@@ -1,4 +1,5 @@
 fn main() {
     let text = include_str!("input.txt");
     println!("{}", day9::part1::solve(text));
+    println!("{}", day9::part2::solve(text));
 }
diff --git a/2023/day9/src/part1.rs b/2023/day9/src/part1.rs
@@ -1,42 +1,15 @@
-fn retain_deltas(mut values: Vec<i32>) -> Vec<i32> {
-    for i in 1..values.len() {
-        values[i - 1] = values[i] - values[i - 1];
-    }
-    values.pop();
-    values
-}
-
-pub fn solve_line(line: &str) -> i32 {
-    let mut values: Vec<i32> = line
-        .split(' ')
-        .map(|s| s.parse().expect("number"))
-        .collect();
-    let mut lasts: Vec<i32> = vec![];
-    while !values.iter().all(|&value| value == 0) {
-        lasts.push(*values.last().expect("loop to end when vec is empty"));
-        values = retain_deltas(values);
-    }
-    lasts.into_iter().sum()
-}
+use crate::row::Row;
 
 pub fn solve(text: &str) -> i32 {
-    text.lines().map(solve_line).sum()
+    text.lines().map(Row::from_line).map(Row::solve).sum()
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
-    const SAMPLE: &str = include_str!("sample.txt");
-
-    #[test]
-    fn solve_line_sample() {
-        for (line, want) in SAMPLE.lines().zip([18, 28, 68]) {
-            assert_eq!(solve_line(line), want);
-        }
-    }
     #[test]
     fn sample() {
-        assert_eq!(solve(SAMPLE), 114);
+        assert_eq!(solve(include_str!("sample.txt")), 114);
     }
 }
diff --git a/2023/day9/src/part2.rs b/2023/day9/src/part2.rs
@@ -0,0 +1,19 @@
+use crate::row::Row;
+
+pub fn solve(text: &str) -> i32 {
+    text.lines()
+        .map(Row::from_line)
+        .map(Row::backward)
+        .map(Row::solve)
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn sample() {
+        assert_eq!(solve(include_str!("sample.txt")), 2);
+    }
+}
diff --git a/2023/day9/src/row.rs b/2023/day9/src/row.rs
@@ -0,0 +1,47 @@
+pub struct Row(Vec<i32>);
+
+impl Row {
+    pub fn from_line(line: &str) -> Row {
+        Row(line
+            .split(' ')
+            .map(|s| s.parse().expect("number"))
+            .collect())
+    }
+
+    pub fn backward(mut self) -> Row {
+        self.0.reverse();
+        self
+    }
+
+    pub fn solve(mut self) -> i32 {
+        let mut sum = 0;
+        while !self.0.iter().all(|&value| value == 0) {
+            for i in 1..self.0.len() {
+                self.0[i - 1] = self.0[i] - self.0[i - 1];
+            }
+            sum += self.0.pop().expect("loop to end if vec is empty");
+        }
+        sum
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &str = include_str!("sample.txt");
+
+    #[test]
+    fn sample() {
+        for (line, want) in SAMPLE.lines().zip([18, 28, 68]) {
+            assert_eq!(Row::from_line(line).solve(), want);
+        }
+    }
+
+    #[test]
+    fn sample_backward() {
+        for (line, want) in SAMPLE.lines().zip([-3, 0, 5]) {
+            assert_eq!(Row::from_line(line).backward().solve(), want);
+        }
+    }
+}