feat: added day 2 part 1 and 2

Signed-off-by: Louis Vallat <contact@louis-vallat.fr>

day2/Cargo.toml

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

day2/src/main.rs

@@ -0,0 +1,64 @@
+use std::{env, fs};
+
+fn read_input(path: &str) -> String {
+    fs::read_to_string(path).expect("Cannot read file.")
+}
+
+fn parse_input(input: &str) -> Vec<Vec<i32>> {
+    input
+        .lines()
+        .filter(|line| !line.is_empty())
+        .map(|line| {
+            line.split(" ")
+                .map(|num| num.parse().expect("Could not parse as i32."))
+                .collect()
+        })
+        .collect()
+}
+
+fn is_safe(levels: &Vec<i32>, allowed_errors: u32) -> bool {
+    if levels.len() < 2 {
+        return true;
+    }
+
+    if levels.len() == 2 {
+        return (1..=3).contains(&(levels[0] - levels[1]).abs())
+    }
+    
+    let mut diff: i32 = levels[1] - levels[2];
+    for i in 1..levels.len() {
+        let local_diff = levels[i - 1] - levels[i];
+        if local_diff.signum() != diff.signum() || !(1..=3).contains(&local_diff.abs()) {
+            return if allowed_errors == 0 {
+                false
+            } else {
+                let mut levels_low = levels.clone();
+                levels_low.remove(i - 1);
+                let mut levels_high = levels.clone();
+                levels_high.remove(i);
+                is_safe(&levels_low, allowed_errors - 1) || is_safe(&levels_high, allowed_errors - 1)
+            }
+        }
+        diff = local_diff;
+    }
+    true
+}
+
+fn part_1(levels: &Vec<Vec<i32>>) -> usize {
+    levels.iter().filter(|level| is_safe(level, 0)).count()
+}
+
+fn part_2(levels: &Vec<Vec<i32>>) -> usize {
+    levels.iter().filter(|level| is_safe(level, 1)).count()
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let input = read_input(&arg);
+        let levels = parse_input(&input);
+        println!("[{}]", &arg);
+        println!("\t[Part 1] => Answer is '{}'.", part_1(&levels));
+        println!("\t[Part 2] => Answer is '{}'.", part_2(&levels));
+    }
+}