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fixed merge sort (#2202)

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* reformat merge sort

* Formatted with Google Java Formatter

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
This commit is contained in:
Du Yuanchao
2021-05-06 17:49:12 +08:00
committed by GitHub
parent 8e228109b1
commit ea123111d9
1 changed files with 24 additions and 28 deletions
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52
Sorts/MergeSort.java
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@ -1,22 +1,18 @@
package Sorts; 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 * @see SortAlgorithm
*/ */
class MergeSort implements 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 unsorted the array which should be sorted.
* @param <T> Comparable class * @param <T> Comparable class.
* @return sorted array * @return sorted array.
*/ */
@Override @Override
public <T extends Comparable<T>> T[] sort(T[] unsorted) { 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 arr the array to be sorted.
* @param left The first index of the array * @param left the first index of the array.
* @param right The last index of the array Recursively sorts the array in increasing order * @param right the last index of the array.
*/ */
private static <T extends Comparable<T>> void doSort(T[] arr, 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) >>> 1;
doSort(arr, left, mid); doSort(arr, left, mid);
doSort(arr, mid + 1, right); doSort(arr, mid + 1, right);
merge(arr, left, mid, 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 arr the array to be merged.
* @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 merges two parts of an array in increasing order * @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) { private static <T extends Comparable<T>> void merge(T[] arr, int left, int mid, int right) {
int length = right - left + 1; int length = right - left + 1;
@SuppressWarnings("unchecked")
T[] temp = (T[]) new Comparable[length]; T[] temp = (T[]) new Comparable[length];
int i = left; int i = left;
int j = mid + 1; int j = mid + 1;
@ -72,21 +69,20 @@ class MergeSort implements SortAlgorithm {
System.arraycopy(temp, 0, arr, left, length); System.arraycopy(temp, 0, arr, left, length);
} }
// Driver program /** Driver code */
public static void main(String[] args) { public static void main(String[] args) {
// Integer Input
Integer[] arr = {4, 23, 6, 78, 1, 54, 231, 9, 12};
MergeSort mergeSort = new MergeSort(); MergeSort mergeSort = new MergeSort();
Integer[] arr = {4, 23, 6, 78, 1, 54, 231, 9, 12};
mergeSort.sort(arr); 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"}; String[] stringArray = {"c", "a", "e", "b", "d"};
mergeSort.sort(stringArray); mergeSort.sort(stringArray);
// Output => a b c d e for (int i = 0; i < stringArray.length - 1; ++i) {
print(stringArray); assert arr[i].compareTo(arr[i + 1]) <= 0;
}
} }
} }