Day2 task 1 finished

Cargo.lock

@@ -9,3 +9,7 @@ version = "0.1.0"
 [[package]]
 name = "day1"
 version = "0.1.0"
+
+[[package]]
+name = "day2"
+version = "0.1.0"

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = ["./day*"]
+members = ["./day*", "day2"]
 
 [package]
 name = "advent_of_code_2024"

day2/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "day2"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

day2/src/common.rs

@@ -0,0 +1,89 @@
+use std::convert::{identity, Infallible};
+use std::str::FromStr;
+
+pub(crate) struct Level(Vec<usize>);
+
+impl FromStr for Level {
+    type Err = Infallible;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Ok(Self(
+            s.split(" ")
+                .filter_map(|value| value.parse::<usize>().ok())
+                .collect::<Vec<_>>(),
+        ))
+    }
+}
+
+impl Level {
+    // TODO optimize
+    pub(crate) fn is_safe(&self) -> bool {
+        (0..self.0.len())
+            .map(|index| Self::is_increasing(&self.0[index..]))
+            .all(identity)
+            || (0..self.0.len())
+                .map(|index| Self::is_decreasing(&self.0[index..]))
+                .all(identity)
+    }
+
+    pub(crate) fn is_increasing(array: &[usize]) -> bool {
+        Self::is_changing(array, PartialOrd::gt)
+    }
+
+    pub(crate) fn is_decreasing(array: &[usize]) -> bool {
+        Self::is_changing(array, PartialOrd::lt)
+    }
+
+    fn is_changing(array: &[usize], operator: fn(&usize, &usize) -> bool) -> bool {
+        match array {
+            [first, second, ..] if operator(second, first) => Self::is_legal_diff(*first, *second),
+            [_singleton] => true,
+            _ => false,
+        }
+    }
+
+    fn is_legal_diff(first: usize, second: usize) -> bool {
+        usize::abs_diff(first, second) >= 1 && usize::abs_diff(first, second) <= 3
+    }
+}
+pub(crate) fn parse_input(input: &str) -> Vec<Level> {
+    input
+        .split("\n")
+        .map(Level::from_str)
+        .collect::<Result<_, _>>()
+        .unwrap()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::common::Level;
+
+    #[test]
+    fn test_is_increasing() {
+        let increasing_array = [1, 2, 3];
+        assert!(Level::is_increasing(&increasing_array))
+    }
+
+    #[test]
+    fn test_is_safe_no_change() {
+        let increasing_then_not = vec![1, 2, 2, 3];
+        assert!(!Level(increasing_then_not).is_safe())
+    }
+
+    #[test]
+    fn test_task_1() {
+        let test_decreasing = vec![7, 6, 4, 2, 1];
+        let test_increase_of_5 = vec![1, 2, 7, 8, 9];
+        let test_decrease_of_4 = vec![9, 7, 6, 2, 1];
+        let test_increase_and_decrease = vec![1, 3, 2, 4, 5];
+        let test_leveled = vec![8, 6, 4, 4, 1];
+        let test_increasing = vec![1, 3, 6, 7, 9];
+
+        assert!(Level(test_decreasing).is_safe());
+        assert!(!Level(test_increase_of_5).is_safe());
+        assert!(!Level(test_decrease_of_4).is_safe());
+        assert!(!Level(test_increase_and_decrease).is_safe());
+        assert!(!Level(test_leveled).is_safe());
+        assert!(Level(test_increasing).is_safe());
+    }
+}

day2/src/main.rs

@@ -0,0 +1,8 @@
+use crate::task1::task1;
+
+mod task1;
+mod common;
+
+fn main() {
+    task1();
+}

day2/src/task1.rs

@@ -0,0 +1,11 @@
+use crate::common::{parse_input, Level};
+
+pub(crate) fn task1() {
+    let raw_input = include_str!("./input.txt");
+    let levels = parse_input(raw_input);
+    let count = levels.into_iter()
+        .filter(Level::is_safe)
+        .count();
+    
+    println!("The solution to task 1 is {}", count)
+}