From 7bb2b390a0cb0a26d9f41c253bae13734e51daec Mon Sep 17 00:00:00 2001
From: Russell Champoux <Russell.Champoux@coupa.com>
Date: Thu, 4 Dec 2025 16:05:29 +0000
Subject: [PATCH] day 03

---
 data/examples/03.txt |  4 +++
 src/bin/03.rs        | 68 ++++++++++++++++++++++++++++++++++++++++++++
 src/template.txt     |  1 +
 3 files changed, 73 insertions(+)
 create mode 100644 data/examples/03.txt
 create mode 100644 src/bin/03.rs

diff --git a/data/examples/03.txt b/data/examples/03.txt
new file mode 100644
index 0000000..7255fca
--- /dev/null
+++ b/data/examples/03.txt
@@ -0,0 +1,4 @@
+987654321111111
+811111111111119
+234234234234278
+818181911112111
diff --git a/src/bin/03.rs b/src/bin/03.rs
new file mode 100644
index 0000000..ed336fc
--- /dev/null
+++ b/src/bin/03.rs
@@ -0,0 +1,68 @@
+advent_of_code::solution!(3);
+
+fn get_largest_battery(battery: &[u32], start_idx: usize, end_idx: usize) -> Option<(u32, usize)> {
+    let mut largest = battery[start_idx];
+    let mut largest_idx = start_idx;
+    for i in start_idx..=end_idx {
+        if battery[i] > largest {
+            largest = battery[i];
+            largest_idx = i;
+        }
+    }
+    Some((largest, largest_idx))
+}
+
+fn get_joltage(line: &str, desired_digits: u8) -> Option<u64> {
+    let all_values = line.chars().into_iter().map(|c| c.to_digit(10).unwrap()).collect::<Vec<u32>>();
+    // determine the largest joltage by finding the largest battery in the list (excluding the last item) and then the largest battery after that
+    let mut total: u64 = 0;
+    let mut start_idx = 0;
+
+    // print!("Calculating joltage for line: {} -> ", line);
+    for i in 1..=desired_digits {
+        let end_idx = all_values.len() - (1 + desired_digits - i) as usize;
+        // print!("Finding largest between {} and {}", start_idx, end_idx);
+        let (largest, largest_idx) = get_largest_battery(&all_values, start_idx, end_idx).unwrap();
+        // println!(" -> found {}", largest);
+        total = total * 10 + largest as u64;
+        start_idx = largest_idx + 1;
+    }
+    Some(total)
+}
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let mut total: u64 = 0;
+    for line in input.split('\n').filter(|l| !l.is_empty()) {
+        total += get_joltage(line, 2).unwrap();
+    }
+
+    println!("Total: {}", total);
+    Some(total)
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let mut total: u64 = 0;
+    for line in input.split('\n').filter(|l| !l.is_empty()) {
+        total += get_joltage(line, 12).unwrap();
+    }
+
+    println!("Total: {}", total);
+    Some(total)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(357));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(3121910778619));
+    }
+}
diff --git a/src/template.txt b/src/template.txt
index 87eac99..c53d29b 100644
--- a/src/template.txt
+++ b/src/template.txt
@@ -1,4 +1,5 @@
 advent_of_code::solution!(%DAY_NUMBER%);
+use itertools::Itertools;
 
 pub fn part_one(input: &str) -> Option<u64> {
     None