Bael 9172

core-java-modules/core-java-collections-list-7/src/main/java/com/baeldung/linkedlistarray/LinkedListArray.java

@@ -0,0 +1,89 @@
+package com.baeldung.linkedlistarray;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+public class LinkedListArray {
+
+    public static LinkedList<Integer>[] groupNumbersUsingRawArray(int[] numbers) {
+        @SuppressWarnings("unchecked") LinkedList<Integer>[] groupListArray = new LinkedList[3];
+
+        for (int i = 0; i < groupListArray.length; i++) {
+            groupListArray[i] = new LinkedList<>();
+        }
+
+        for (int num : numbers) {
+            if (num < 10) {
+                groupListArray[0].add(num);
+            } else if (num < 20) {
+                groupListArray[1].add(num);
+            } else {
+                groupListArray[2].add(num);
+            }
+        }
+        return groupListArray;
+    }
+
+    public static List<LinkedList<Integer>> groupNumbersUsingListOfLinkedList(int[] numbers) {
+        List<LinkedList<Integer>> groupListArray = new ArrayList<>();
+
+        for (int i = 0; i < 3; i++) {
+            groupListArray.add(new LinkedList<>());
+        }
+
+        for (int num : numbers) {
+            if (num < 10) {
+                groupListArray.get(0)
+                    .add(num);
+            } else if (num < 20) {
+                groupListArray.get(1)
+                    .add(num);
+            } else {
+                groupListArray.get(2)
+                    .add(num);
+            }
+        }
+        return groupListArray;
+    }
+
+    public static List<LinkedList<Integer>> groupNumbersUsingStreams(int[] numbers) {
+        List<LinkedList<Integer>> groupListArray = IntStream.range(0, 3)
+            .mapToObj(i -> new LinkedList<Integer>())
+            .collect(Collectors.toList());
+
+        for (int num : numbers) {
+            if (num < 10) {
+                groupListArray.get(0)
+                    .add(num);
+            } else if (num < 20) {
+                groupListArray.get(1)
+                    .add(num);
+            } else {
+                groupListArray.get(2)
+                    .add(num);
+            }
+        }
+        return groupListArray;
+    }
+
+    public static LinkedList<Integer>[] groupNumbersUsingSetAll(int[] numbers) {
+        @SuppressWarnings("unchecked") LinkedList<Integer>[] groupListArray = new LinkedList[3];
+        Arrays.setAll(groupListArray, i -> new LinkedList<>());
+
+        for (int num : numbers) {
+            if (num < 10) {
+                groupListArray[0].add(num);
+            } else if (num < 20) {
+                groupListArray[1].add(num);
+            } else {
+                groupListArray[2].add(num);
+            }
+        }
+        return groupListArray;
+    }
+}
+

core-java-modules/core-java-collections-list-7/src/test/java/com/baeldung/linkedlistarray/LinkedListArrayUnitTest.java

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+package com.baeldung.linkedlistarray;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.LinkedList;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+public class LinkedListArrayUnitTest {
+
+    @Test
+    void givenNumbers_whenGroupedUsingRawArray_thenGroupsAreCorrect() {
+        int[] input = { 3, 11, 21, 9, 19, 22 };
+        LinkedList<Integer>[] arrayOfLists = LinkedListArray.groupNumbersUsingRawArray(input);
+
+        assertEquals(2, arrayOfLists[0].size());
+        assertTrue(arrayOfLists[0].contains(3));
+        assertTrue(arrayOfLists[0].contains(9));
+    }
+
+    @Test
+    void givenNumbers_whenGroupedUsingLinkedList_thenGroupsAreCorrect() {
+        int[] input = { 3, 11, 21, 9, 19, 22 };
+        List<LinkedList<Integer>> arrayOfLists = LinkedListArray.groupNumbersUsingListOfLinkedList(input);
+
+        assertEquals(2, arrayOfLists.get(1)
+            .size());
+        assertTrue(arrayOfLists.get(1)
+            .contains(11));
+        assertTrue(arrayOfLists.get(1)
+            .contains(19));
+    }
+
+    @Test
+    void givenNumbers_whenGroupedUsingStreams_thenGroupsAreCorrect() {
+        int[] input = { 3, 11, 21, 9, 19, 22 };
+        List<LinkedList<Integer>> arrayOfLists = LinkedListArray.groupNumbersUsingStreams(input);
+
+        assertEquals(2, arrayOfLists.get(0)
+            .size());
+        assertTrue(arrayOfLists.get(0)
+            .contains(3));
+        assertTrue(arrayOfLists.get(0)
+            .contains(9));
+    }
+
+    @Test
+    void givenNumbers_whenGroupedUsingSetAll_thenGroupsAreCorrect() {
+        int[] input = { 3, 11, 21, 9, 19, 22 };
+        LinkedList<Integer>[] arrayOfLists = LinkedListArray.groupNumbersUsingSetAll(input);
+
+        assertEquals(2, arrayOfLists[2].size());
+        assertTrue(arrayOfLists[2].contains(21));
+        assertTrue(arrayOfLists[2].contains(22));
+    }
+}