CrazyLambdas upgrade

* complete comparing and thenComparing method

Author: tboychuk

5-0-functional-programming/5-1-1-crazy-lambdas/src/main/java/com/bobocode/fp/CrazyLambdas.java

@@ -265,7 +265,7 @@ public static BiFunction<Map<String, IntUnaryOperator>, String, IntUnaryOperator
      * @return a comparator instance
      */
     public static <T, U extends Comparable<? super U>> Comparator<T> comparing(Function<? super T, ? extends U> mapper) {
-        throw new ExerciseNotCompletedException();
+        return (o1, o2) -> mapper.apply(o1).compareTo(mapper.apply(o2));
     }
 
     /**
@@ -285,7 +285,13 @@ public static <T, U extends Comparable<? super U>> Comparator<T> comparing(Funct
      */
     public static <T, U extends Comparable<? super U>> Comparator<T> thenComparing(
             Comparator<? super T> comparator, Function<? super T, ? extends U> mapper) {
-        throw new ExerciseNotCompletedException();
+        return (o1, o2) -> {
+            var initialResult = comparator.compare(o1, o2);
+            if (initialResult != 0) {
+                return initialResult;
+            }
+            return mapper.apply(o1).compareTo(mapper.apply(o2));
+        };
     }
 
     /**