From ea123111d91ed2fbd418b10af50124b96d4f7587 Mon Sep 17 00:00:00 2001
From: Du Yuanchao <shellhub.me@gmail.com>
Date: Thu, 6 May 2021 17:49:12 +0800
Subject: [PATCH] fixed merge sort (#2202)

* reformat merge sort

* Formatted with Google Java Formatter

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
---
 Sorts/MergeSort.java | 52 ++++++++++++++++++++------------------------
 1 file changed, 24 insertions(+), 28 deletions(-)

diff --git a/Sorts/MergeSort.java b/Sorts/MergeSort.java
index dfd350afb..57892bc6b 100644
--- a/Sorts/MergeSort.java
+++ b/Sorts/MergeSort.java
@@ -1,22 +1,18 @@
 package Sorts;
 
-import static Sorts.SortUtils.print;
-
 /**
- * This method implements the Generic Merge Sort
+ * Generic merge sort algorithm.
  *
- * @author Varun Upadhyay (https://github.com/varunu28)
- * @author Podshivalov Nikita (https://github.com/nikitap492)
  * @see SortAlgorithm
  */
 class MergeSort implements SortAlgorithm {
 
   /**
-   * This method implements the Generic Merge Sort
+   * Generic merge sort algorithm implements.
    *
-   * @param unsorted the array which should be sorted
-   * @param <T> Comparable class
-   * @return sorted array
+   * @param unsorted the array which should be sorted.
+   * @param <T> Comparable class.
+   * @return sorted array.
    */
   @Override
   public <T extends Comparable<T>> T[] sort(T[] unsorted) {
@@ -25,13 +21,13 @@ class MergeSort implements SortAlgorithm {
   }
 
   /**
-   * @param arr The array to be sorted
-   * @param left The first index of the array
-   * @param right The last index of the array Recursively sorts the array in increasing order
+   * @param arr the array to be sorted.
+   * @param left the first index of the array.
+   * @param right the last index of the array.
    */
   private static <T extends Comparable<T>> void doSort(T[] arr, int left, int right) {
     if (left < right) {
-      int mid = left + (right - left) / 2;
+      int mid = (left + right) >>> 1;
       doSort(arr, left, mid);
       doSort(arr, mid + 1, right);
       merge(arr, left, mid, right);
@@ -39,15 +35,16 @@ class MergeSort implements SortAlgorithm {
   }
 
   /**
-   * This method implements the merge step of the merge sort
+   * Merges two parts of an array.
    *
-   * @param arr The array to be sorted
-   * @param left The first index of the array
-   * @param mid The middle index of the array
-   * @param right The last index of the array merges two parts of an array in increasing order
+   * @param arr the array to be merged.
+   * @param left the first index of the array.
+   * @param mid the middle index of the array.
+   * @param right the last index of the array merges two parts of an array in increasing order.
    */
   private static <T extends Comparable<T>> void merge(T[] arr, int left, int mid, int right) {
     int length = right - left + 1;
+    @SuppressWarnings("unchecked")
     T[] temp = (T[]) new Comparable[length];
     int i = left;
     int j = mid + 1;
@@ -72,21 +69,20 @@ class MergeSort implements SortAlgorithm {
     System.arraycopy(temp, 0, arr, left, length);
   }
 
-  // Driver program
+  /** Driver code */
   public static void main(String[] args) {
-
-    // Integer Input
-    Integer[] arr = {4, 23, 6, 78, 1, 54, 231, 9, 12};
     MergeSort mergeSort = new MergeSort();
+
+    Integer[] arr = {4, 23, 6, 78, 1, 54, 231, 9, 12};
     mergeSort.sort(arr);
+    for (int i = 0; i < arr.length - 1; ++i) {
+      assert arr[i] <= arr[i + 1];
+    }
 
-    // Output => 1	   4  	 6	9	12	23	54	78	231
-    print(arr);
-
-    // String Inpu
     String[] stringArray = {"c", "a", "e", "b", "d"};
     mergeSort.sort(stringArray);
-    // Output => a	b	c	d	e
-    print(stringArray);
+    for (int i = 0; i < stringArray.length - 1; ++i) {
+      assert arr[i].compareTo(arr[i + 1]) <= 0;
+    }
   }
 }