2nd day

Author: majcn

data/examples/02.txt

@@ -0,0 +1,6 @@
+7 6 4 2 1
+1 2 7 8 9
+9 7 6 2 1
+1 3 2 4 5
+8 6 4 4 1
+1 3 6 7 9

src/bin/02.rs

@@ -0,0 +1,108 @@
+advent_of_code::solution!(2);
+
+use advent_of_code::maneatingape::parse::*;
+
+fn parse_data(input: &str) -> Vec<Vec<i32>> {
+    input
+        .lines()
+        .map(|line| line.iter_signed().collect())
+        .collect()
+}
+
+fn is_valid_pair(x: i32, y: i32, inc: bool) -> bool {
+    let diff = if inc { y - x } else { x - y };
+
+    (1..=3).contains(&diff)
+}
+
+fn find_broken_position<'a, I>(mut iter: I) -> Option<usize>
+where
+    I: Iterator<Item = &'a i32>,
+{
+    let first = *iter.next().unwrap();
+    let second = *iter.next().unwrap();
+    let inc = second > first;
+
+    if !is_valid_pair(first, second, inc) {
+        return Some(0);
+    }
+
+    let mut x = second;
+    let mut i = 1;
+    for &next_x in iter {
+        if !is_valid_pair(x, next_x, inc) {
+            return Some(i);
+        }
+
+        x = next_x;
+        i += 1;
+    }
+
+    None
+}
+
+fn find_broken_position_with_problem_dampener(line: &[i32]) -> Option<usize> {
+    match find_broken_position(line.iter()) {
+        Some(pos) => {
+            let left = &line[..pos];
+            let right = &line[pos + 1..];
+            find_broken_position(left.iter().chain(right.iter()))?;
+
+            if pos > 0 {
+                let left = &line[..pos - 1];
+                let right = &line[pos..];
+                find_broken_position(left.iter().chain(right.iter()))?;
+            }
+
+            if pos < line.len() {
+                let left = &line[..pos + 1];
+                let right = &line[pos + 2..];
+                find_broken_position(left.iter().chain(right.iter()))?;
+            }
+
+            Some(pos)
+        }
+        None => None,
+    }
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let data = parse_data(input);
+
+    let result = data
+        .into_iter()
+        .map(|line| find_broken_position(line.iter()))
+        .filter(|x| x.is_none())
+        .count();
+
+    Some(result)
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    let data = parse_data(input);
+
+    let result = data
+        .into_iter()
+        .map(|line| find_broken_position_with_problem_dampener(&line))
+        .filter(|x| x.is_none())
+        .count();
+
+    Some(result)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(2));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(4));
+    }
+}