Days 1-5

src/3-lobby.rs

@@ -0,0 +1,37 @@
+use std::{fs::File, io::{self, BufRead, BufReader}};
+
+fn max_joltage(s: &str) -> u64 {
+    let values = s.chars()
+        .map(|x| x.to_digit(10).unwrap())
+        .collect::<Vec<_>>();
+
+    let max_idx = |xs: &[u32]| {
+        xs.iter()
+            .enumerate()
+            .fold(0, |max, (i, &x)| {
+                if x > xs[max] { i } else { max }
+            })
+    };
+
+    let (_, total) =
+        (0..12).rev().fold(
+            (0, 0u64),
+            |(start_idx, total), i| {
+                let next_idx = start_idx + max_idx(&values[start_idx..values.len() - i]);
+                (next_idx + 1, 10 * total + values[next_idx] as u64)
+            }
+        );
+    total
+}
+
+fn main() -> Result<(), io::Error> {
+    let f = File::open("3-input.txt")?;
+    let reader = BufReader::new(f);
+
+    let mut total: u64 = 0;
+    for line in reader.lines() {
+        total += max_joltage(line?.as_str()) as u64;
+    }
+    println!("Result: {}", total);
+    Ok(())
+}