Add solution 1.2

aufgaben/sheet1/sol2/collatz.rs

@@ -0,0 +1,21 @@
+//! Aufgabe 1.2: Collatz
+
+fn main() {
+    // Hardcoding the input value is ugly, but it's fine for now.
+    let mut n = 27;
+    let mut count = 0;
+
+    while n > 1 {
+        // We use the feature "everything is an expression" here to slightly
+        // shorten the code, although, when the task was due, this feature was
+        // not yet introduced to the students.
+        n = if n % 2 == 0 {
+            n / 2
+        } else {
+            n * 3 + 1
+        };
+        count += 1;
+
+        println!("{} -> {}", count, n);
+    }
+}