From a402156786ef23a7f71510a2ac0d42713e3932b3 Mon Sep 17 00:00:00 2001
From: Russell Champoux <Russell.Champoux@coupa.com>
Date: Thu, 4 Dec 2025 17:11:46 -0500
Subject: [PATCH] Solve Day 2: Gift Shop

---
 README.md            |   3 +-
 data/examples/02.txt |   2 +
 src/bin/02.rs        | 110 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 114 insertions(+), 1 deletion(-)
 create mode 100644 data/examples/02.txt
 create mode 100644 src/bin/02.rs

diff --git a/README.md b/README.md
index 70af4d3..2562a95 100644
--- a/README.md
+++ b/README.md
@@ -12,8 +12,9 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 | Day | Part 1 | Part 2 |
 | :---: | :---: | :---:  |
 | [Day 1](./src/bin/01.rs) | `113.0µs` | `119.9µs` |
+| [Day 2](./src/bin/02.rs) | `54.7ms` | `71.6ms` |
 
-**Total: 0.23ms**
+**Total: 126.53ms**
 <!--- benchmarking table --->
 
 ---
diff --git a/data/examples/02.txt b/data/examples/02.txt
new file mode 100644
index 0000000..871da5e
--- /dev/null
+++ b/data/examples/02.txt
@@ -0,0 +1,2 @@
+11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124
+
diff --git a/src/bin/02.rs b/src/bin/02.rs
new file mode 100644
index 0000000..8d1722c
--- /dev/null
+++ b/src/bin/02.rs
@@ -0,0 +1,110 @@
+advent_of_code::solution!(2);
+
+/// Check if a number is "invalid" - made of a pattern repeated exactly twice
+fn is_invalid_part1(n: u64) -> bool {
+    let s = n.to_string();
+    let len = s.len();
+    // Must have even length for pattern to repeat exactly twice
+    if len % 2 != 0 {
+        return false;
+    }
+    let half = len / 2;
+    s[..half] == s[half..]
+}
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let mut sum = 0u64;
+
+    // Parse comma-separated ranges, handling potential whitespace/newlines
+    for part in input.split(',') {
+        let part = part.trim();
+        if part.is_empty() {
+            continue;
+        }
+
+        // Parse "start-end" range
+        let mut range_parts = part.split('-');
+        let start: u64 = range_parts.next()?.parse().ok()?;
+        let end: u64 = range_parts.next()?.parse().ok()?;
+
+        // Check each number in the range
+        for n in start..=end {
+            if is_invalid_part1(n) {
+                sum += n;
+            }
+        }
+    }
+
+    Some(sum)
+}
+
+/// Check if a number is "invalid" - made of a pattern repeated at least twice
+fn is_invalid_part2(n: u64) -> bool {
+    let s = n.to_string();
+    let len = s.len();
+
+    // Try each possible pattern length (1 to len/2)
+    for pattern_len in 1..=len / 2 {
+        // Pattern can only work if it divides evenly
+        if len % pattern_len != 0 {
+            continue;
+        }
+
+        let pattern = &s[..pattern_len];
+        let mut is_match = true;
+
+        // Check if the entire string is made of this pattern repeated
+        for i in (pattern_len..len).step_by(pattern_len) {
+            if &s[i..i + pattern_len] != pattern {
+                is_match = false;
+                break;
+            }
+        }
+
+        if is_match {
+            return true;
+        }
+    }
+
+    false
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let mut sum = 0u64;
+
+    for part in input.split(',') {
+        let part = part.trim();
+        if part.is_empty() {
+            continue;
+        }
+
+        let mut range_parts = part.split('-');
+        let start: u64 = range_parts.next()?.parse().ok()?;
+        let end: u64 = range_parts.next()?.parse().ok()?;
+
+        for n in start..=end {
+            if is_invalid_part2(n) {
+                sum += n;
+            }
+        }
+    }
+
+    Some(sum)
+}
+
+#[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(1227775554));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(4174379265));
+    }
+}