[BAEL-6823] middle of array (#14696)

Co-authored-by: Bhaskar <bhaskar.dastidar@freshworks.com>

core-java-modules/core-java-arrays-operations-advanced/src/main/java/com/baeldung/arraymiddle/MiddleOfArray.java

@@ -0,0 +1,65 @@
+package com.baeldung.arraymiddle;
+
+import java.util.Arrays;
+
+import org.apache.commons.lang3.ObjectUtils;
+
+public class MiddleOfArray {
+    int[] middleOfArray(int[] array) {
+        if (ObjectUtils.isEmpty(array) || array.length < 3)
+            return array;
+        int n = array.length;
+        int mid = n / 2;
+        if (n % 2 == 0) {
+            int mid2 = mid - 1;
+            return new int[] { array[mid2], array[mid] };
+        } else {
+            return new int[] { array[mid] };
+        }
+    }
+
+    int[] middleOfArrayWithStartEndNaive(int[] array, int start, int end) {
+        int mid = (start + end) / 2;
+        int n = end - start;
+        if (n % 2 == 0) {
+            int mid2 = mid - 1;
+            return new int[] { array[mid2], array[mid] };
+        } else {
+            return new int[] { array[mid] };
+        }
+    }
+
+    int[] middleOfArrayWithStartEnd(int[] array, int start, int end) {
+        int mid = start + (end - start) / 2;
+        int n = end - start;
+        if (n % 2 == 0) {
+            int mid2 = mid - 1;
+            return new int[] { array[mid2], array[mid] };
+        } else {
+            return new int[] { array[mid] };
+        }
+    }
+
+    int[] middleOfArrayWithStartEndBitwise(int[] array, int start, int end) {
+        int mid = (start + end) >>> 1;
+        int n = end - start;
+        if (n % 2 == 0) {
+            int mid2 = mid - 1;
+            return new int[] { array[mid2], array[mid] };
+        } else {
+            return new int[] { array[mid] };
+        }
+    }
+
+    int medianOfArray(int[] array, int start, int end) {
+        Arrays.sort(array); // for safety. This can be ignored
+        int mid = (start + end) >>> 1;
+        int n = end - start;
+        if (n % 2 == 0) {
+            int mid2 = mid - 1;
+            return (array[mid2] + array[mid]) / 2;
+        } else {
+            return array[mid];
+        }
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraymiddle/MiddleOfArrayUnitTest.java

@@ -0,0 +1,89 @@
+package com.baeldung.arraymiddle;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class MiddleOfArrayUnitTest {
+
+    @Test
+    public void givenArrayOfEvenLength_whenMiddleOfArray_thenReturn2Values() {
+        int[] array = new int[100];
+        for (int i = 0; i < array.length; i++) {
+            array[i] = i + 1;
+        }
+        int[] expectedMidArray = { 50, 51 };
+        MiddleOfArray middleOfArray = new MiddleOfArray();
+        Assert.assertArrayEquals(expectedMidArray, middleOfArray.middleOfArray(array));
+    }
+
+    @Test
+    public void givenArrayOfEdgeCaseLength_whenMiddleOfArray_thenReturn2Values() {
+        int[] array = new int[0];
+        int[] expectedMidArray = new int[0];
+        MiddleOfArray middleOfArray = new MiddleOfArray();
+        Assert.assertArrayEquals(expectedMidArray, middleOfArray.middleOfArray(array));
+
+        array = new int[] { 1, 2 };
+        expectedMidArray = new int[] { 1, 2 };
+
+        Assert.assertArrayEquals(expectedMidArray, middleOfArray.middleOfArray(array));
+    }
+
+    @Test
+    public void givenArrayOfOddLength_whenMiddleOfArray_thenReturnMid() {
+        int[] array = new int[99];
+        for (int i = 0; i < array.length; i++) {
+            array[i] = i + 1;
+        }
+        int[] expectedMidArray = { 50 };
+        MiddleOfArray middleOfArray = new MiddleOfArray();
+        Assert.assertArrayEquals(expectedMidArray, middleOfArray.middleOfArray(array));
+    }
+
+    @Test
+    public void givenArrayWithStartAndEnd_whenMiddleOfArray_thenReturnMid() {
+        int[] array = new int[100];
+        for (int i = 0; i < array.length; i++) {
+            array[i] = i + 1;
+        }
+        int[] expectedMidArray = { 58 };
+        MiddleOfArray middleOfArray = new MiddleOfArray();
+        Assert.assertArrayEquals(expectedMidArray, middleOfArray.middleOfArrayWithStartEndNaive(array, 55, 60));
+
+        expectedMidArray = new int[] { 58, 59 };
+        Assert.assertArrayEquals(expectedMidArray, middleOfArray.middleOfArrayWithStartEndNaive(array, 56, 60));
+    }
+
+    @Test
+    public void givenArrayWithStartAndEndOptimized_whenMiddleOfArray_thenReturnMid() {
+        int[] array = new int[100];
+        for (int i = 0; i < array.length; i++) {
+            array[i] = i + 1;
+        }
+        int[] expectedMidArray = { 78 };
+        MiddleOfArray middleOfArray = new MiddleOfArray();
+        Assert.assertArrayEquals(expectedMidArray, middleOfArray.middleOfArrayWithStartEnd(array, 55, 100));
+    }
+
+    @Test
+    public void givenArrayWithStartAndEndBitwise_whenMiddleOfArray_thenReturnMid() {
+        int[] array = new int[100];
+        for (int i = 0; i < array.length; i++) {
+            array[i] = i + 1;
+        }
+        int[] expectedMidArray = { 78 };
+        MiddleOfArray middleOfArray = new MiddleOfArray();
+        Assert.assertArrayEquals(expectedMidArray, middleOfArray.middleOfArrayWithStartEndBitwise(array, 55, 100));
+    }
+
+    @Test
+    public void givenArrayWithStartAndEnd_whenMedianOfArray_thenReturnMid() {
+        int[] array = new int[100];
+        for (int i = 0; i < array.length; i++) {
+            array[i] = i + 1;
+        }
+        int expectMedian = 50;
+        MiddleOfArray middleOfArray = new MiddleOfArray();
+        Assert.assertEquals(expectMedian, middleOfArray.medianOfArray(array, 0, 100));
+    }
+}