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Author: professorDeveloper

src/MergeSortApp.java

@@ -0,0 +1,65 @@
+package sorting;
+
+import java.util.Arrays;
+
+public class MergeSortApp {
+
+    //https://t.me/leetcodin/332
+    //Time complexity: O(N * logN)
+    //Space complexity: O(N)
+    private static class MergeSort {
+        private int[] array;
+
+        public void mergeSort(int[] arr) {
+            array = arr;
+            int len = array.length;
+            int[] workspace = new int[len];
+            recursiveMergeSort(workspace, 0, len - 1);
+        }
+
+        private void recursiveMergeSort(int[] workSpace, int lowerBound,
+                                        int upperBound) {
+            if (lowerBound == upperBound) {
+                return;
+            } else {
+                int mid = (lowerBound + upperBound) / 2;
+                recursiveMergeSort(workSpace, lowerBound, mid);
+                recursiveMergeSort(workSpace, mid + 1, upperBound);
+                merge(workSpace, lowerBound, mid + 1, upperBound);
+            }
+        }
+
+        private void merge(int[] workspace, int lowPointer,
+                           int highPointer, int upperBound) {
+            int i = 0;
+            int lowerBound = lowPointer;
+            int mid = highPointer - 1;
+            int numberOfItems = upperBound - lowerBound + 1;
+
+            while (lowPointer <= mid && highPointer <= upperBound) {
+                if (array[lowPointer] < array[highPointer]) {
+                    workspace[i++] = array[lowPointer++];
+                } else {
+                    workspace[i++] = array[highPointer++];
+                }
+            }
+
+            while (lowPointer <= mid)
+                workspace[i++] = array[lowPointer++];
+
+            while (highPointer <= upperBound)
+                workspace[i++] = array[highPointer++];
+
+            for (i = 0; i < numberOfItems; i++)
+                array[lowerBound + i] = workspace[i];
+        }
+    }
+
+    public static void main(String[] args) {
+        MergeSort mergeSort = new MergeSort();
+        int[] arr = new int[]{6, 5, 3, 1, 8, 7, 2, 4};
+        System.out.println("Before: " + Arrays.toString(arr));
+        mergeSort.mergeSort(arr);
+        System.out.println("After: " + Arrays.toString(arr));
+    }
+}