feat: completed solutions

exercises/20_threads/threads1.rs

@@ -20,10 +20,12 @@ fn main() {
         handles.push(handle);
     }
 
-    let mut results = Vec::new();
+    let mut results: Vec<_> = Vec::<_>::new();
+
     for handle in handles {
         // TODO: Collect the results of all threads into the `results` vector.
         // Use the `JoinHandle` struct which is returned by `thread::spawn`.
+        results.push(handle.join().unwrap())
     }
 
     if results.len() != 10 {