optimization

Author: realDuYuanChao

Sorts/MergeSort.java

@@ -22,24 +22,22 @@ class MergeSort implements SortAlgorithm {
  @Override
  @SuppressWarnings("unchecked")
  public <T extends Comparable<T>> T[] sort(T[] unsorted) {
- T[] tmp = (T[]) new Comparable[unsorted.length];
- doSort(unsorted, tmp, 0, unsorted.length - 1);
+ doSort(unsorted, 0, unsorted.length - 1);
  return unsorted;
  }
 
  /**
  * @param arr The array to be sorted
- * @param temp The copy of the actual array
  * @param left The first index of the array
  * @param right The last index of the array
  * Recursively sorts the array in increasing order
  **/
- private static <T extends Comparable<T>> void doSort(T[] arr, T[] temp, int left, int right) {
+ private static <T extends Comparable<T>> void doSort(T[] arr, int left, int right) {
  if (left < right) {
  int mid = left + (right - left) / 2;
- doSort(arr, temp, left, mid);
- doSort(arr, temp, mid + 1, right);
- merge(arr, temp, left, mid, right);
+ doSort(arr, left, mid);
+ doSort(arr, mid + 1, right);
+ merge(arr, left, mid, right);
  }
 
  }
@@ -48,36 +46,36 @@ private static <T extends Comparable<T>> void doSort(T[] arr, T[] temp, int left
  * This method implements the merge step of the merge sort
  *
  * @param arr The array to be sorted
- * @param temp The copy of the actual array
  * @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, T[] temp, int left, int mid, int right) {
- System.arraycopy(arr, left, temp, left, right - left + 1);
-
-
+ private static <T extends Comparable<T>> void merge(T[] arr, int left, int mid, int right) {
+ int length = right - left + 1;
+ T[] temp = (T[]) new Comparable[length];
  int i = left;
  int j = mid + 1;
- int k = left;
+ int k = 0;
 
  while (i <= mid && j <= right) {
- if (temp[i].compareTo(temp[j]) <= 0) {
- arr[k++] = temp[i++];
+ if (arr[i].compareTo(arr[j]) <= 0) {
+ temp[k++] = arr[i++];
  } else {
- arr[k++] = temp[j++];
+ temp[k++] = arr[j++];
  }
  }
 
  while (i <= mid) {
- arr[k++] = temp[i++];
+ temp[k++] = arr[i++];
  }
 
  while (j <= right) {
- arr[k++] = temp[j++];
+ temp[k++] = arr[j++];
  }
+
+ System.arraycopy(temp, 0, arr, left, length);
  }
 
  // Driver program