Algorithms/JavaAlgorithms
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optimization

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shellhub 2020-01-09 18:28:56 +08:00
parent a60cb58be8
commit dc6f830d07
1 changed files with 16 additions and 18 deletions
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34
Sorts/MergeSort.java
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@ -22,24 +22,22 @@ class MergeSort implements SortAlgorithm {
@Override @Override
@SuppressWarnings("unchecked") @SuppressWarnings("unchecked")
public <T extends Comparable<T>> T[] sort(T[] unsorted) { public <T extends Comparable<T>> T[] sort(T[] unsorted) {
T[] tmp = (T[]) new Comparable[unsorted.length]; doSort(unsorted, 0, unsorted.length - 1);
doSort(unsorted, tmp, 0, unsorted.length - 1);
return unsorted; return unsorted;
} }
/** /**
* @param arr The array to be sorted * @param arr The array to be sorted
* @param temp The copy of the actual array
* @param left The first index of the array * @param left The first index of the array
* @param right The last index of the array * @param right The last index of the array
* Recursively sorts the array in increasing order * 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) { if (left < right) {
int mid = left + (right - left) / 2; int mid = left + (right - left) / 2;
doSort(arr, temp, left, mid); doSort(arr, left, mid);
doSort(arr, temp, mid + 1, right); doSort(arr, mid + 1, right);
merge(arr, temp, left, mid, right); merge(arr, left, mid, right);
} }
} }
@ -48,36 +46,36 @@ class MergeSort implements SortAlgorithm {
* This method implements the merge step of the merge sort * This method implements the merge step of the merge sort
* *
* @param arr The array to be sorted * @param arr The array to be sorted
* @param temp The copy of the actual array
* @param left The first index of the array * @param left The first index of the array
* @param mid The middle index of the array * @param mid The middle index of the array
* @param right The last index of the array * @param right The last index of the array
* merges two parts of an array in increasing order * 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) { private static <T extends Comparable<T>> void merge(T[] arr, int left, int mid, int right) {
System.arraycopy(arr, left, temp, left, right - left + 1); int length = right - left + 1;
T[] temp = (T[]) new Comparable[length];
int i = left; int i = left;
int j = mid + 1; int j = mid + 1;
int k = left; int k = 0;
while (i <= mid && j <= right) { while (i <= mid && j <= right) {
if (temp[i].compareTo(temp[j]) <= 0) { if (arr[i].compareTo(arr[j]) <= 0) {
arr[k++] = temp[i++]; temp[k++] = arr[i++];
} else { } else {
arr[k++] = temp[j++]; temp[k++] = arr[j++];
} }
} }
while (i <= mid) { while (i <= mid) {
arr[k++] = temp[i++]; temp[k++] = arr[i++];
} }
while (j <= right) { while (j <= right) {
arr[k++] = temp[j++]; temp[k++] = arr[j++];
} }
System.arraycopy(temp, 0, arr, left, length);
} }
// Driver program // Driver program