Solve 02

src/bin/02.rs

@@ -0,0 +1,65 @@
+use aoc::*;
+use itertools::Itertools;
+
+const INPUT: &str = include_str!("../../input/02");
+
+fn main() {
+    assert_example!(part1, "02-test", 2);
+    println!("Part 1: {}", part1(INPUT));
+    assert_example!(part2, "02-test", 4);
+    println!("Part 2: {}", part2(INPUT));
+}
+
+fn part1(input: &str) -> usize {
+    parse(input)
+        .into_iter()
+        .filter(|report| is_safe(report))
+        .count()
+}
+
+fn part2(input: &str) -> usize {
+    parse(input)
+        .into_iter()
+        .filter(|report| is_dampened_safe(report))
+        .count()
+}
+
+fn is_safe(report: &[i64]) -> bool {
+    let monotonic = decreasing(report) || increasing(report);
+    monotonic && not_steep(report)
+}
+
+fn is_dampened_safe(report: &[i64]) -> bool {
+    (0..report.len()).any(|i| {
+        let mut report = report.to_owned();
+        report.remove(i);
+        is_safe(&report)
+    })
+}
+
+fn increasing(report: &[i64]) -> bool {
+    gradient(report).all(|n| n > 0)
+}
+
+fn decreasing(report: &[i64]) -> bool {
+    gradient(report).all(|n| n < 0)
+}
+
+fn not_steep(report: &[i64]) -> bool {
+    gradient(report).all(|n| n.abs() <= 3)
+}
+
+fn gradient(report: &[i64]) -> impl Iterator<Item = i64> + use<'_> {
+    report.iter().copied().tuple_windows().map(|(a, b)| b - a)
+}
+
+fn parse(input: &str) -> Vec<Vec<i64>> {
+    input.lines().map(parse_line).collect()
+}
+
+fn parse_line(input: &str) -> Vec<i64> {
+    input
+        .split_whitespace()
+        .map(|n| n.parse().unwrap())
+        .collect()
+}