Solve 2025 day 3 part 1 in rust

2025/rust/day-03/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day-03"
+version = "0.1.0"

2025/rust/day-03/Cargo.toml

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+[package]
+name = "day-03"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

2025/rust/day-03/src/main.rs

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+use std::fs;
+
+fn main() {
+    let banks = parse_input(&fs::read_to_string("../../inputs/03.txt").unwrap());
+
+    println!("Total output joltage: {}", total_joltage(banks));
+}
+
+fn parse_input(contents: &str) -> Vec<Vec<u8>> {
+    contents
+        .trim()
+        .lines()
+        .map(|line: &str| line.bytes().map(|b| b - b'0').collect())
+        .collect()
+}
+
+fn total_joltage(banks: Vec<Vec<u8>>) -> u32 {
+    banks.iter().map(|bank| largest_joltage(bank)).sum()
+}
+
+fn largest_joltage(batteries: &[u8]) -> u32 {
+    let mut first = batteries[0];
+    let mut second = batteries[1];
+
+    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];
+        }
+    }
+
+    (first * 10 + second) as u32
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = "987654321111111
+811111111111119
+234234234234278
+818181911112111
+";
+
+    #[test]
+    fn test_part1() {
+        assert_eq!(total_joltage(parse_input(TEST_INPUT)), 357);
+    }
+}