added recursive merge sort practice problem

Author: ARajan1084

src/com/codefortomorrow/advanced/chapter13/practice/RecurMergeSort.java

@@ -0,0 +1,7 @@
+package com.codefortomorrow.advanced.chapter13.practice;
+
+public class RecurMergeSort {
+    public static void recurMergeSort(Comparable[] array, int start, int end) {
+
+    }
+}

src/com/codefortomorrow/advanced/chapter13/solutions/RecurMergeSort.java

@@ -0,0 +1,41 @@
+package com.codefortomorrow.advanced.chapter13.solutions;
+
+public class RecurMergeSort {
+    public static void recurMergeSort(Comparable[] array, int start, int end) {
+        if (start >= end) {
+            return;
+        }
+        int middle = (start + end) / 2;
+        recurMergeSort(array, start, middle);
+        recurMergeSort(array, middle + 1, end);
+        int i = start;
+        int j = middle + 1;
+        Comparable[] sortedArray = new Comparable[end - start + 1];
+        int k = 0;
+        while (i <= middle && j <= end) {
+            if (array[i].compareTo(array[j]) > 0) {
+                sortedArray[k] = array[i];
+                i++;
+            } else {
+                sortedArray[k] = array[j];
+                j++;
+            }
+            k++;
+        }
+        while (i <= middle) {
+            sortedArray[k] = array[i];
+            i++;
+            k++;
+        }
+        while (j <= end) {
+            sortedArray[k] = array[j];
+            j++;
+            k++;
+        }
+        k = 0;
+        for (int l = start; l <= end; l++) {
+            array[l] = sortedArray[k];
+            k++;
+        }
+    }
+}