add lookup table

2021/src/day8.rs

@@ -58,6 +58,14 @@ impl SegmentSet {
     fn len(&self) -> u8 {
         self.len
     }
+
+    fn union(&self, other: &Self) -> Self {
+        self.data | other.data
+    }
+
+    fn intersect(&self, other: &Self) -> Self {
+        self.data & other.data
+    }
 }
 
 impl FromStr for SegmentSet {
@@ -95,6 +103,21 @@ impl FromStr for Screen {
 }
 
 
+const DIGIT_SEGMENTS = {
+    let segment_strs = [
+        "abcefg", "cf", "acdeg", "acdfg",
+        "bcdf", "abdfg", "abdefg", "acf",
+        "abcdefg", "abcdfg",
+    ]
+
+    let sets = [SegmentSet::default(), 10]
+    for (i, s) in segment_strs.iter().enumerate() {
+        sets[i] = s.parse::<SegmentSet>().unwrap()
+    }
+    sets
+}
+
+
 fn part1(screens: &[Screen]) -> usize {
     screens.iter()
         .flat_map(|d| d.output.iter())