Solve Day 2: Gift Shop

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));
+    }
+}