Solve day 9

day09/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "day09"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+aoc-utils = { path = "../aoc-utils" }

day09/src/main.rs

@@ -0,0 +1,109 @@
+use aoc_utils::PuzzleInput;
+const DAY: u8 = 9;
+
+fn main() {
+    let input = PuzzleInput::get_input(DAY);
+    println!("A: {}", solve_a(&input));
+    println!("B: {}", solve_b(&input));
+}
+
+fn parse_numbers(line: String) -> Vec<i64> {
+    line.split_whitespace()
+        .map(|s| s.parse::<i64>().unwrap())
+        .collect()
+}
+
+fn calculate_diffs(history: Vec<i64>) -> Vec<Vec<i64>> {
+    let mut difference_vecs: Vec<Vec<i64>> = Vec::new();
+    difference_vecs.push(history.clone());
+
+    while !difference_vecs.last().unwrap().iter().all(|v| *v == 0) {
+        let mut difference_vec = Vec::new();
+        let previous_diffs = difference_vecs.last().unwrap();
+        for i in 0..previous_diffs.len() - 1 {
+            difference_vec.push(previous_diffs[i + 1] - previous_diffs[i]);
+        }
+        difference_vecs.push(difference_vec);
+    }
+
+    difference_vecs
+}
+
+fn predict_next_value(history: Vec<i64>) -> i64 {
+    let mut difference_vecs: Vec<Vec<i64>> = calculate_diffs(history);
+
+    // Compute the next difference for each order
+    difference_vecs.last_mut().unwrap().push(0);
+    for i in (0..difference_vecs.len() - 1).rev() {
+        let new_value = {
+            let current_history = &difference_vecs[i];
+            let higher_history = &difference_vecs[i + 1];
+
+            current_history.last().unwrap() + higher_history.last().unwrap()
+        };
+
+        difference_vecs[i].push(new_value);
+    }
+
+    *difference_vecs.first().unwrap().last().unwrap()
+}
+
+fn predict_previous_value(history: Vec<i64>) -> i64 {
+    let mut difference_vecs: Vec<Vec<i64>> = calculate_diffs(history);
+
+    difference_vecs.last_mut().unwrap().push(0);
+    for i in (0..difference_vecs.len() - 1).rev() {
+        let new_value = {
+            let current_history = &difference_vecs[i];
+            let higher_history = &difference_vecs[i + 1];
+
+            current_history.first().unwrap() - higher_history.first().unwrap()
+        };
+
+        difference_vecs[i].insert(0, new_value);
+    }
+
+    *difference_vecs.first().unwrap().first().unwrap()
+}
+
+fn solve_a(input: &PuzzleInput) -> i64 {
+    input
+        .lines()
+        .map(|line| parse_numbers(line.to_string()))
+        .map(predict_next_value)
+        .sum()
+}
+
+fn solve_b(input: &PuzzleInput) -> i64 {
+    input
+        .lines()
+        .map(|line| parse_numbers(line.to_string()))
+        .map(predict_previous_value)
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = "0 3 6 9 12 15
+1 3 6 10 15 21
+10 13 16 21 30 45";
+
+    #[test]
+    fn test_no_panic() {
+        let input = PuzzleInput::get_input(DAY);
+        solve_a(&input);
+        solve_b(&input);
+    }
+
+    #[test]
+    fn test_solve_a() {
+        assert_eq!(solve_a(&PuzzleInput::new(TEST_INPUT)), 114);
+    }
+
+    #[test]
+    fn test_solve_b() {
+        assert_eq!(solve_b(&PuzzleInput::new(TEST_INPUT)), 2);
+    }
+}