Add solution sheet7

aufgaben/sheet7/sol1/fib.rs

@@ -0,0 +1,31 @@
+struct Fib {
+    curr: u64,
+    last: u64,
+}
+
+impl Fib {
+    fn new() -> Self {
+        Fib {
+            curr: 1,
+            last: 0,
+        }
+    }
+}
+
+impl Iterator for Fib {
+    type Item = u64;
+    fn next(&mut self) -> Option<Self::Item> {
+        let new = self.last + self.curr;
+        self.last = self.curr;
+        self.curr = new;
+
+        Some(self.last)
+    }
+}
+
+
+fn main() {
+    for i in Fib::new().take(20) {
+        println!("{}", i);
+    }
+}