2016 day 9

aoc16/src/main.rs

@@ -44,6 +44,7 @@ fn main() {
         6 => solve_day!(day06, &input),
         7 => solve_day!(day07, &input),
         8 => solve_day!(day08, &input),
+        9 => solve_day!(day09, &input),
         _ => println!("day not solved: {}", day),
     }
 }

aoc16/src/solutions.rs

@@ -5,4 +5,5 @@ pub mod day04;
 pub mod day05;
 pub mod day06;
 pub mod day07;
-pub mod day08;
+pub mod day08;
+pub mod day09;

aoc16/src/solutions/day09.rs

@@ -0,0 +1,102 @@
+pub fn part1(input: &str) -> usize {
+    input.lines().map(decompress).map(|s| s.len()).sum()
+}
+
+pub fn part2(input: &str) -> usize {
+    input.lines().map(fully_decompressed_length).sum()
+}
+
+fn decompress(compressed: &str) -> String {
+    let mut decompressed = String::new();
+    let mut chars = compressed.chars();
+
+    while let Some(ch) = chars.next() {
+        if ch == '(' {
+            let (amount, times) = extract_marker(&mut chars);
+            decompressed.push_str(&repeat(&mut chars, amount, times));
+        } else {
+            decompressed.push(ch);
+        }
+    }
+
+    decompressed
+}
+
+fn extract_marker(chars: &mut impl Iterator<Item = char>) -> (usize, usize) {
+    let mut marker = String::new();
+
+    for ch in chars.by_ref() {
+        if ch == ')' {
+            break;
+        }
+        marker.push(ch);
+    }
+
+    let (amount, times) = marker.split_once('x').unwrap();
+    (amount.parse().unwrap(), times.parse().unwrap())
+}
+
+fn repeat(chars: &mut impl Iterator<Item = char>, amount: usize, times: usize) -> String {
+    chars.take(amount).collect::<String>().repeat(times)
+}
+
+fn fully_decompressed_length(line: &str) -> usize {
+    decrompressed_length_helper(&mut line.chars(), 1)
+}
+
+fn decrompressed_length_helper(
+    mut section: &mut impl Iterator<Item = char>,
+    multiplier: usize,
+) -> usize {
+    let mut result = 0;
+
+    while let Some(ch) = section.next() {
+        if ch == '(' {
+            let (amount, times) = extract_marker(&mut section);
+
+            let taken = section.take(amount).collect::<String>();
+            result += decrompressed_length_helper(&mut taken.chars(), multiplier * times);
+        } else {
+            result += multiplier;
+        }
+    }
+
+    result
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn find_marker_test() {
+        assert_eq!((1, 5), extract_marker(&mut "1x5)BC".chars()));
+    }
+
+    #[test]
+    fn decrompress_test() {
+        assert_eq!("ADVENT".to_string(), decompress("ADVENT"));
+        assert_eq!("ABBBBBC".to_string(), decompress("A(1x5)BC"));
+        assert_eq!("XYZXYZXYZ".to_string(), decompress("(3x3)XYZ"));
+        assert_eq!("ABCBCDEFEFG".to_string(), decompress("A(2x2)BCD(2x2)EFG"));
+        assert_eq!("(1x3)A".to_string(), decompress("(6x1)(1x3)A"));
+        assert_eq!(
+            "X(3x3)ABC(3x3)ABCY".to_string(),
+            decompress("X(8x2)(3x3)ABCY")
+        );
+    }
+
+    #[test]
+    fn fully_decompressed_length_test() {
+        assert_eq!(9, fully_decompressed_length("(3x3)XYZ"));
+        assert_eq!(20, fully_decompressed_length("X(8x2)(3x3)ABCY"));
+        assert_eq!(
+            241920,
+            fully_decompressed_length("(27x12)(20x12)(13x14)(7x10)(1x12)A")
+        );
+        assert_eq!(
+            445,
+            fully_decompressed_length("(25x3)(3x3)ABC(2x3)XY(5x2)PQRSTX(18x9)(3x2)TWO(5x7)SEVEN")
+        );
+    }
+}