Initial data commit

Task/Flatten-a-list/Java/flatten-a-list-1.java

@@ -0,0 +1,22 @@
+import java.util.LinkedList;
+import java.util.List;
+
+
+public final class FlattenUtil {
+
+	public static List<Object> flatten(List<?> list) {
+		List<Object> retVal = new LinkedList<Object>();
+		flatten(list, retVal);
+		return retVal;
+	}
+
+	public static void flatten(List<?> fromTreeList, List<Object> toFlatList) {
+		for (Object item : fromTreeList) {
+			if (item instanceof List<?>) {
+				flatten((List<?>) item, toFlatList);
+			} else {
+				toFlatList.add(item);
+			}
+		}
+	}
+}

Task/Flatten-a-list/Java/flatten-a-list-2.java

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+import static java.util.Arrays.asList;
+import java.util.List;
+
+public final class FlattenTestMain {
+
+	public static void main(String[] args) {
+		List<Object> treeList = a(a(1), 2, a(a(3, 4), 5), a(a(a())), a(a(a(6))), 7, 8, a());
+		List<Object> flatList = FlattenUtil.flatten(treeList);
+		System.out.println(treeList);
+		System.out.println("flatten: " + flatList);
+	}
+	
+	private static List<Object> a(Object... a) {
+		return asList(a);
+	}
+}

Task/Flatten-a-list/Java/flatten-a-list-3.java

@@ -0,0 +1,17 @@
+import java.util.List;
+import java.util.stream.Stream;
+import java.util.stream.Collectors;
+
+public final class FlattenUtil {
+
+	public static Stream<Object> flattenToStream(List<?> list) {
+		return list.stream().flatMap(item ->
+			item instanceof List<?> ?
+			flattenToStream((List<?>)item) :
+			Stream.of(item));
+	}
+
+	public static List<Object> flatten(List<?> list) {
+		return flattenToStream(list).collect(Collectors.toList());
+	}
+}