completed day 3, ready for day 4.

src/day02/utilities.rs

@@ -0,0 +1,40 @@
+#[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{
+    //play enum has value corresponding to its score.
+    let mut score = input.you as usize;
+    //an enum wins if (you-elf)%3 = 1, looses if it = 2
+    let gamestatus = (input.you as i8 - input.elf as i8).rem_euclid(3);
+    match gamestatus {
+        1 => score+=6,
+        2 => (),
+        0 => score += 3,
+        _ => panic!("gamestatus was {}!, you were {}, elf was {}", gamestatus, input.you as i8, input.elf as i8)
+    }
+    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);
+    }
+}