add solution to day3 challenge

Rust/rustifinity/adventofrust/day3.rs

@@ -0,0 +1,17 @@
+pub const GOOD_WEIGHT: f32 = 1.0;
+pub const BAD_WEIGHT: f32 = 2.0;
+
+pub fn is_nice(good_deeds: u32, bad_deeds: u32) -> bool {
+    let good_deeds = good_deeds as f32;
+    let bad_deeds = bad_deeds as f32;
+
+    if good_deeds == 0 && bad_deeds == 0 {
+        return false;
+    }
+    let ratio = good_deeds / ((good_deeds * GOOD_WEIGHT) + (bad_deeds * BAD_WEIGHT));
+    if ratio >= 0.75 {
+        return true;
+    } else {
+        return false;
+    }
+}