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Jan 10, 2020
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optimization #1201

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34 changes: 16 additions & 18 deletions Sorts/MergeSort.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
}

}
Expand All @@ -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
Expand Down