Day9 Rust

day9/rust/src/main.rs

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+enum Direction {
+    Forward,
+    Backward,
+}
+
+fn main() {
+    let stdin = std::io::stdin();
+
+    let mut part1 = 0;
+    let mut part2 = 0;
+
+    for line in stdin.lines() {
+        let line = line.unwrap();
+
+        let history = line.split(" ").map(|e| e.parse().unwrap()).collect();
+
+        part1 += extrapolate(&history, Direction::Forward);
+        part2 += extrapolate(&history, Direction::Backward);
+    }
+
+    println!("{}", part1);
+    println!("{}", part2);
+}
+
+fn extrapolate(history: &Vec<isize>, direction: Direction) -> isize {
+    if history.iter().all(|e| *e == 0) {
+        return 0;
+    }
+
+    let new_history = history.windows(2).map(|pair| pair[1] - pair[0]).collect();
+
+    if let Direction::Forward = direction {
+        return history.last().unwrap() + extrapolate(&new_history, direction);
+    }
+
+    return history[0] - extrapolate(&new_history, direction);
+}