day 2

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 +1,76 @@
+advent_of_code::solution!(2);
+
+fn is_safe(levels: &[i32]) -> bool {
+    let is_increasing = levels.windows(2).all(|pair| pair[1] > pair[0]);
+    let is_decreasing = levels.windows(2).all(|pair| pair[1] < pair[0]);
+
+    if !is_increasing && !is_decreasing {
+        return false;
+    }
+
+    levels.windows(2).all(|pair| {
+        let diff = (pair[1] - pair[0]).abs();
+        (1..=3).contains(&diff)
+    })
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let count = input
+        .lines()
+        .filter(|report| {
+            let levels: Vec<i32> = report
+                .split_whitespace()
+                .map(|n| n.parse::<i32>().expect("Invalid number"))
+                .collect();
+
+            is_safe(&levels)
+        })
+        .count();
+
+    Some(count as u32)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let count = input
+        .lines()
+        .filter(|report| {
+            let levels: Vec<i32> = report
+                .split_whitespace()
+                .map(|n| n.parse::<i32>().expect("Invalid number"))
+                .collect();
+
+            if is_safe(&levels) {
+                return true;
+            }
+
+            for i in 0..levels.len() {
+                let mut modified = levels.clone();
+                modified.remove(i);
+
+                if is_safe(&modified) {
+                    return true;
+                }
+            }
+            false
+        })
+        .count();
+
+    Some(count as u32)
+}
+
+#[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));
+    }
+}