Start day 2

src/main.rs

@@ -12,8 +12,9 @@ fn main() -> std::io::Result<()> {
         return Ok(());
     }
 
-    match u8::from_str(&args.next().unwrap()) {
+    match u8::from_str(&args.nth(1).unwrap()) {
         Ok(1) => solutions::day_1::run(args)?,
+        Ok(2) => solutions::day_2::run(args)?,
         Ok(_) => eprintln!("Unknown day. Are you from the future?"),
         Err(_) => eprintln!("Unknown day format. Use integers to specify."),
     }

src/solutions/day_2.rs

@@ -0,0 +1,61 @@
+use std::cmp::Ordering;
+use std::env;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::str::FromStr;
+
+pub fn run(mut args: env::Args) -> std::io::Result<()> {
+    let filename = args
+        .next()
+        .expect("You must provide a filename as argument");
+
+    let f = File::open(filename)?;
+    let reader = BufReader::new(f);
+
+    let mut num_safe = 0;
+
+    for line in reader.lines() {
+        let l = line.unwrap();
+        if l.is_empty() {
+            continue;
+        }
+
+        let levels: Vec<u8> = l
+            .split_whitespace()
+            .map(u8::from_str)
+            .map(Result::unwrap)
+            .collect();
+
+        if levels.len() <= 1 {
+            if levels.len() == 1 {
+                num_safe += 1;
+            }
+            continue;
+        }
+
+        let ord = levels[0].cmp(&levels[1]);
+        if ord != Ordering::Equal {
+            let mut safe = true;
+            for i in 1..levels.len() {
+                let abs_diff = levels[i - 1].abs_diff(levels[i]);
+                if levels[i - 1].cmp(&levels[i]) != ord || abs_diff > 3 {
+                    // the case that the difference is < 1 is caught by cmp as it will return ==
+                    safe = false;
+                    break;
+                }
+            }
+
+            if safe {
+                num_safe += 1;
+            }
+        }
+    }
+
+    // Task 1
+    println!("Number of safe levels: {num_safe}");
+
+    // Task 2
+    // TBD
+
+    Ok(())
+}

src/solutions/mod.rs

@@ -1,2 +1,3 @@
 pub mod day_1;
+pub mod day_2;