Day 2

Author: jacob-greenfield

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 +1,70 @@
+use advent_of_code::template::parse::splitn;
+
+advent_of_code::solution!(2);
+
+pub fn part_one(input: &str) -> Option<u32> {
+    Some(
+        splitn::<u32>(input)
+            .map(|report| {
+                if report.len() < 2 {
+                    1
+                } else {
+                    let increase = report[0] < report[1];
+                    if report
+                        .iter()
+                        .zip(report[1..].iter())
+                        .all(|(&a, &b)| (1..=3).contains(&a.abs_diff(b)) && (a < b) == increase)
+                    {
+                        1
+                    } else {
+                        0
+                    }
+                }
+            })
+            .sum(),
+    )
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    Some(
+        splitn::<u32>(input)
+            .map(|report| {
+                if report.len() < 3 {
+                    1
+                } else {
+                    let mut sub = vec![];
+                    if (0..report.len()).any(|bad_idx| {
+                        sub.clear();
+                        sub.extend_from_slice(&report[..bad_idx]);
+                        sub.extend_from_slice(&report[(bad_idx + 1)..]);
+                        let increase = sub[0] < sub[1];
+                        sub.iter()
+                            .zip(sub[1..].iter())
+                            .all(|(&a, &b)| (1..=3).contains(&a.abs_diff(b)) && (a < b) == increase)
+                    }) {
+                        1
+                    } else {
+                        0
+                    }
+                }
+            })
+            .sum(),
+    )
+}
+
+#[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));
+    }
+}

src/template/parse.rs

@@ -148,6 +148,21 @@ pub fn split5<
     })
 }
 
+/// Parse some number items from each line, separated by ASCII whitespace
+pub fn splitn<'a, T: MyFromStr<'a>>(input: &'a str) -> impl 'a + Iterator<Item = Vec<T>> {
+    lines(input).filter_map(|line| {
+        let mut parts = line.split_ascii_whitespace();
+        let Some(part0) = parts.next() else {
+            // skip blank lines
+            cold();
+            return None;
+        };
+        let mut vec = vec![part0.my_parse().unwrap()];
+        vec.extend(parts.map(|part| part.my_parse().unwrap()));
+        Some(vec)
+    })
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;