1 files changed, 81 insertions, 0 deletions

diff --git a/day8/src/main.rs b/day8/src/main.rs
new file mode 100644
index 0000000..8e90063
--- /dev/null
+++ b/day8/src/main.rs
@@ -0,0 +1,81 @@
+use std::fs;
+use std::path::Path;
+use std::collections::HashMap;
+
+/* AOC21 Day 8: https://adventofcode.com/2021/day/8 */
+fn main() {
+    let input = Path::new("resources").join("input.txt");
+    let content = fs::read_to_string(input).expect("Unable to read input file");
+    println!("Ex1: The result is {}", ex1(&content));
+    println!("Ex2: The result is {}", ex2(&content));
+}
+
+fn ex1(content: &str) -> usize {
+    content.lines().flat_map(
+       |l| l.split_once(" | ").expect("Malformed input").1.split_whitespace().map(|d| d.len())
+    ).filter(|&x| x == 2 || x == 3 || x == 4 || x == 7).count()
+}
+
+#[inline]
+fn parse_pattern(pattern: &str) -> (usize,u8) {
+    (pattern.len(), pattern.bytes().fold(0, |a, b| a + (1 << (b - b'a'))))
+}
+
+fn decode_patterns(patterns: &[(usize,u8)]) -> HashMap<u8,u32> {
+    let mut map = [0; 10];
+    patterns.iter().for_each(|(l,e)| {
+        match l {
+            2 => map[1] = *e,
+            3 => map[7] = *e,
+            4 => map[4] = *e,
+            7 => map[8] = *e,
+            _ => {}
+        }
+    });
+    patterns.iter().for_each(|(l,e)| {
+        match l {
+            5 if (e & map[1]).count_ones() == 2 => map[3] = *e,
+            5 if (e & map[4]).count_ones() == 2 => map[2] = *e,
+            5 => map[5] = *e,
+            6 if (e & map[4]).count_ones() == 4 => map[9] = *e,
+            6 if (e & map[1]).count_ones() == 2 => map[0] = *e,
+            6 => map[6] = *e,
+            _ => {}
+        }
+    });
+    map.iter().enumerate().fold(HashMap::new(),|mut m, (i,v)| { m.insert(*v, i as u32); m })
+}
+
+fn ex2(content: &str) -> u32 {
+    content.lines().map(|l| {
+        let (patterns, digits) = l.split_once(" | ").expect("Malformed input");
+        let patterns = decode_patterns(&patterns.split_whitespace().map(|p| parse_pattern(p)).collect::<Vec<(usize,u8)>>());
+        digits.split_whitespace().map(|p| patterns.get(&parse_pattern(p).1).unwrap()).fold(0, |a,d| (a*10)+d)
+    }).sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const INPUT: &str = "be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb | fdgacbe cefdb cefbgd gcbe
+edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec | fcgedb cgb dgebacf gc
+fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg
+fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega | efabcd cedba gadfec cb
+aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga | gecf egdcabf bgf bfgea
+fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf | gebdcfa ecba ca fadegcb
+dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf | cefg dcbef fcge gbcadfe
+bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbgef
+egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb
+gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce";
+
+    #[test]
+    fn example1() {
+        assert_eq!(26, ex1(INPUT))
+    }
+
+    #[test]
+    fn example2() {
+        assert_eq!(61229, ex2(INPUT))
+    }
+}