switched to workspaces.

This should let me make a cross-day library.

days/day02/src/utilities.rs

@@ -0,0 +1,36 @@
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum Play {
+    Rock = 1,
+    Paper = 2,
+    Scissors = 3,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct Strategy {
+    pub elf: Play,
+    pub you: Play,
+}
+
+pub fn calc_score(input: &Strategy) -> usize {
+    //an enum wins if (you-elf)%3 = 1, looses if it = 2
+    (match (input.you as i8 - input.elf as i8).rem_euclid(3) {
+        1 => 6,
+        2 => 0,
+        0 => 3,
+        _ => unreachable!("you were {}, elf was {}", input.you as i8, input.elf as i8),
+    }) + input.you as usize //play enum has value corresponding to its score.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_calc_score() {
+        let input = Strategy {
+            elf: Play::Scissors,
+            you: Play::Scissors,
+        };
+        assert_eq!(calc_score(&input), 6);
+    }
+}