1 files changed, 46 insertions, 0 deletions
diff --git a/src/day3.rs b/src/day3.rs
new file mode 100644
index 0000000..5c01b7a
--- /dev/null
+++ b/src/day3.rs
@@ -0,0 +1,46 @@
+use std::{collections::{HashSet, HashMap}};
+
+pub fn run(input: String) {
+    if !input.is_ascii() {
+        panic!("input wasn't ascii, character calculations won't work!");
+    }
+
+    let scores_table = make_scores_table();
+
+    let ll: Vec<&str> = input.lines().collect();
+    
+    let score = ll.chunks(3).map(|gm| {
+        let init: Option<HashSet<char>> = None;
+        let lb: Vec<char> = gm.into_iter().fold(init, |maybe_acc, m| {
+            let cs: HashSet<char> = m.chars().collect();
+            if let Some(acc) = maybe_acc {
+                let rr: HashSet<char> = acc.intersection(&cs).map(|x| {x.clone()}).collect();
+                Some(rr)
+            } else {
+                Some(cs)
+            }
+        })
+            .expect("didn't get any group members??!")
+            .into_iter().collect();
+        let ct = lb.len();
+        if ct != 1 {
+            panic!("Couldn't find exactly one badge for group! found {}, {:?}", ct, gm);
+        }
+        let ch = lb.into_iter().next().expect("foo");
+        scores_table.get(&ch).expect(format!("couldn't find score for char {}", ch).as_str())
+    }).sum::<u32>();
+    println!("Day 3: {}", score);
+}
+
+fn make_scores_table() -> HashMap<char, u32> {
+    let mut scores_table: HashMap<char,u32> = HashMap::new();
+    let r1 = 'a'..='z';
+    for (ix, ch) in r1.enumerate() {
+        scores_table.insert(ch, (ix as u32)+1);
+    }
+    let r2 = 'A'..='Z';
+    for (ix, ch) in r2.enumerate() {
+        scores_table.insert(ch, (ix as u32)+27);
+    }
+    scores_table
+}
+\ No newline at end of file