From c7683b36008fbea06cb02510b7ec6875a15158a4 Mon Sep 17 00:00:00 2001
From: SebastianStork <git@sstork.dev>
Date: Wed, 3 Dec 2025 19:09:15 +0100
Subject: [PATCH] Solve 2025 day 3 part 2 in rust

---
 2025/rust/day-03/src/main.rs | 44 +++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/2025/rust/day-03/src/main.rs b/2025/rust/day-03/src/main.rs
index 693512b..a4e079d 100644
--- a/2025/rust/day-03/src/main.rs
+++ b/2025/rust/day-03/src/main.rs
@@ -3,7 +3,8 @@ use std::fs;
 fn main() {
     let banks = parse_input(&fs::read_to_string("../../inputs/03.txt").unwrap());
 
-    println!("Total output joltage: {}", total_joltage(banks));
+    println!("Total output joltage: {}", total_joltage(&banks, 2));
+    println!("New total output joltage: {}", total_joltage(&banks, 12));
 }
 
 fn parse_input(contents: &str) -> Vec<Vec<u8>> {
@@ -14,24 +15,31 @@ fn parse_input(contents: &str) -> Vec<Vec<u8>> {
         .collect()
 }
 
-fn total_joltage(banks: Vec<Vec<u8>>) -> u32 {
-    banks.iter().map(|bank| largest_joltage(bank)).sum()
+fn total_joltage(banks: &[Vec<u8>], number_of_activate_batteries: usize) -> u64 {
+    banks
+        .iter()
+        .map(|bank| largest_joltage(bank, number_of_activate_batteries))
+        .sum()
 }
 
-fn largest_joltage(batteries: &[u8]) -> u32 {
-    let mut first = batteries[0];
-    let mut second = batteries[1];
+fn largest_joltage(batteries: &[u8], number_of_activate_batteries: usize) -> u64 {
+    let mut active_batteries: Vec<u8> = batteries[0..number_of_activate_batteries].into();
 
-    for i in 1..batteries.len() - 1 {
-        if batteries[i] > first {
-            first = batteries[i];
-            second = batteries[i + 1];
-        } else if batteries[i + 1] > second {
-            second = batteries[i + 1];
+    for i in 1..batteries.len() - (number_of_activate_batteries - 1) {
+        for j in 0..number_of_activate_batteries {
+            if batteries[j + i] > active_batteries[j] {
+                active_batteries[j..number_of_activate_batteries]
+                    .copy_from_slice(&batteries[j + i..number_of_activate_batteries + i]);
+            }
         }
     }
 
-    (first * 10 + second) as u32
+    active_batteries
+        .iter()
+        .rev()
+        .enumerate()
+        .map(|(i, joltage)| *joltage as u64 * 10_u64.pow(i as u32))
+        .sum()
 }
 
 #[cfg(test)]
@@ -41,11 +49,15 @@ mod tests {
     const TEST_INPUT: &str = "987654321111111
 811111111111119
 234234234234278
-818181911112111
-";
+818181911112111";
 
     #[test]
     fn test_part1() {
-        assert_eq!(total_joltage(parse_input(TEST_INPUT)), 357);
+        assert_eq!(total_joltage(&parse_input(TEST_INPUT), 2), 357);
+    }
+
+    #[test]
+    fn test_part2() {
+        assert_eq!(total_joltage(&parse_input(TEST_INPUT), 12), 3121910778619);
     }
 }