Add mergesort java impl

MergeSort.java

@@ -0,0 +1,59 @@
+/*
+ * Mergesort impl in Java.
+ * Input: An array over integers that has to be sorted
+ * Output: Sorted Array over integers
+ */
+
+public class MergeSort {
+
+    public static void mergeSort(int[] arrToSort, int n) {
+
+        if (n < 2) {
+            return;
+        }
+
+        // Find the middle point to divide the array into two halves
+        int mid = n / 2;
+
+        // Divide the payload
+        int[] left = new int[mid];
+        int[] right = new int[n - mid];
+
+        for (int i = 0; i < mid; i++) {
+            left[i] = arrToSort[i];
+        }
+
+        for (int i = mid; i < n; i++) {
+            right[i - mid] = arrToSort[i];
+        }
+
+        // Call mergeSort for first half
+        mergeSort(left, mid);
+        // Call mergeSort for second half
+        mergeSort(right, n - mid);
+        // Merge the two halves sorted
+        merge(arrToSort, left, right, mid, n - mid);
+    }
+
+    public static void merge(int[] arrToSort, int[] left, int[] right, int lbound, int rbound) {
+
+        int i = 0, j = 0, k = 0;
+
+        while (i < lbound && j < rbound) {
+            if (left[i] <= right[j]) {
+                arrToSort[k++] = left[i++];
+            }
+            else {
+                arrToSort[k++] = right[j++];
+            }
+        }
+
+        while (i < lbound) {
+            arrToSort[k++] = left[i++];
+        }
+
+        while (j < rbound) {
+            arrToSort[k++] = right[j++];
+        }
+    }
+}

MergeSortTest.java

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+import org.junit.Test;
+
+import java.util.Arrays;
+
+import static org.junit.Assert.assertArrayEquals;
+
+public class MergeSortTest {
+    @Test
+    public void should_evaluate_to_true() {
+        int[] actual = { 5, 1, 6, 2, 3, 4 };
+        int[] expected = { 1, 2, 3, 4, 5, 6 };
+        System.out.println("Array before applying mergesort: " + Arrays.toString(actual));
+        MergeSort.mergeSort(actual, actual.length);
+        System.out.println("Array after applying mergesort: " + Arrays.toString(actual));
+        assertArrayEquals(expected, actual);
+    }
+}