solution: 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 +1,81 @@
+use itertools::Itertools;
+
+fn parse_input(input: &str) -> impl Iterator<Item = Vec<isize>> + '_ {
+    input.lines().map(|l| {
+        l.split(' ')
+            .filter_map(|x| x.parse::<isize>().ok())
+            .collect_vec()
+    })
+}
+
+fn check_report(mut r: impl Iterator<Item = isize>) -> bool {
+    let mut low = 0;
+    let mut high = 0;
+
+    let mut prev = r.next().expect("Invalid input file?");
+
+    for n in r {
+        let diff = n - prev;
+        prev = n;
+
+        if diff == 0 {
+            return false;
+        };
+
+        if !(-3..=3).contains(&diff) {
+            return false;
+        }
+
+        if diff > 0 {
+            high += 1;
+        }
+
+        if diff < 0 {
+            low += 1;
+        }
+    }
+
+    !(low > 0 && high > 0)
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    parse_input(input)
+        .map(|r| check_report(r.into_iter()))
+        .filter(|&x| x)
+        .count()
+        .into()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    Some(
+        parse_input(input)
+            .map(|r| {
+                (0..r.len()).any(|i| {
+                    check_report(
+                        // skip nth idx
+                        r.iter()
+                            .enumerate()
+                            .filter(|&(j, _)| j != i)
+                            .map(|(_, &v)| v),
+                    )
+                })
+            })
+            .filter(|x| *x)
+            .count(),
+    )
+}
+
+aoc::solution!(2);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(part_one(&aoc::template::read_file("examples", 2)), None);
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(part_two(&aoc::template::read_file("examples", 2)), None);
+    }
+}