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MergeSort.java
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50 lines (44 loc) · 1.26 KB
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import java.util.Arrays;
public class MergeSort {
public static void main(String[] args) {
int[] arr = {9,3,4,2,1};
sort(arr);
System.out.println(Arrays.toString(arr));
}
public static void sort(int[] arr) {
if (arr == null || arr.length < 2) {
return;
}
final int sz = arr.length;
int[] aux = new int[sz];
msort(arr, 0, sz - 1, aux);
}
private static void msort(int[] arr, int start, int end, int[] aux) {
if (start >= end) {
return;
}
int mid = start + (end - start) / 2;
msort(arr, start, mid, aux);
msort(arr, mid + 1, end, aux);
merge(arr, start, mid, end, aux);
}
private static void merge(int[] arr, int start, int mid, int end, int[] aux) {
for (int k = start; k <= end; k++) {
aux[k] = arr[k];
}
int i = start, j = mid + 1, k = start;
while (i <= mid && j <= end) {
if (aux[i] < aux[j]) {
arr[k++] = aux[i++];
} else {
arr[k++] = aux[j++];
}
}
while (i <= mid) {
arr[k++] = aux[i++];
}
while (j <= end) {
arr[k++] = aux[j++];
}
}
}