Performance improvement for List::unfold, List::unfoldLeft (#2689)

Author: sleepytomcat

vavr/src/main/java/io/vavr/collection/List.java

@@ -712,7 +712,8 @@ static <T, U> List<U> unfoldRight(T seed, Function<? super T, Option<Tuple2<? ex
      * @throws NullPointerException if {@code f} is null
      */
     static <T, U> List<U> unfoldLeft(T seed, Function<? super T, Option<Tuple2<? extends T, ? extends U>>> f) {
-        return Iterator.unfoldLeft(seed, f).toList();
+        return Iterator.unfoldRight(seed, f.andThen(tupleOpt -> tupleOpt.map(Tuple2::swap)))
+          .foldLeft(List.empty(), List::prepend);
     }
 
     /**
@@ -740,7 +741,8 @@ static <T, U> List<U> unfoldLeft(T seed, Function<? super T, Option<Tuple2<? ext
      * @throws NullPointerException if {@code f} is null
      */
     static <T> List<T> unfold(T seed, Function<? super T, Option<Tuple2<? extends T, ? extends T>>> f) {
-        return Iterator.unfold(seed, f).toList();
+        return Iterator.unfoldRight(seed, f.andThen(tupleOpt -> tupleOpt.map(Tuple2::swap)))
+          .foldLeft(List.empty(), List::prepend);
     }
 
     @Override