Add solution for "Day 3: Lobby", part 2

src/solvers/lobby.rs

@@ -4,20 +4,24 @@ use std::io::BufRead;
 pub struct Lobby {}
 
 impl Lobby {
-    fn largest_joltage(bank: &str) -> u64 {
-        let mut best = (0, 0);
-        for d in bank.bytes().take(bank.len() - 1) {
-            if best.0 < d {
-                best = (d, 0)
-            } else if best.1 < d {
-                best.1 = d;
+    const PART1_MAX_BATTERIES: usize = 2;
+    const PART2_MAX_BATTERIES: usize = 12;
+
+    fn largest_joltage(bank: &str, max_batteries: usize) -> u64 {
+        let mut best = vec![0_u8; max_batteries];
+        for (i, d) in bank.bytes().map(|c| c - '0' as u8).enumerate() {
+            let mut fill_index = max_batteries;
+            let skip = (max_batteries + i).saturating_sub(bank.len());
+            for (j, b) in best.iter_mut().skip(skip).enumerate() {
+                if *b < d {
+                    *b = d;
+                    fill_index = j + 1 + skip;
+                    break;
+                }
             }
+            best[fill_index..].fill(0);
         }
-        let last = bank.bytes().last().unwrap();
-        if best.1 < last {
-            best.1 = last;
-        }
-        u64::from((best.0 - '0' as u8) * 10 + (best.1 - '0' as u8))
+        u64::from(best.iter().fold(0, |acc: u64, &x| acc * 10 + u64::from(x)))
     }
 }
 
@@ -26,10 +30,11 @@ impl Solver for Lobby {
     const PUZZLE_NAME: &'static str = "Lobby";
 
     fn process_data<R: BufRead>(&self, reader: R) -> (u64, u64) {
-        let mut joltage = 0;
+        let mut joltages = (0, 0);
         for line in reader.lines().map_while(Result::ok) {
-            joltage += Self::largest_joltage(&line);
+            joltages.0 += Self::largest_joltage(&line, Self::PART1_MAX_BATTERIES);
+            joltages.1 += Self::largest_joltage(&line, Self::PART2_MAX_BATTERIES);
         }
-        (joltage, 0)
+        joltages
     }
 }