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public class MergeSort {
public static void sort(Comparable[] a) {
Comparable[] aux = new Comparable[a.length];
sort(a, aux, 0, a.length - 1);
}
private static void sort(Comparable[] a, Comparable[] aux, int lo, int hi) {
if (lo >= hi) { //注意判断,否者会造成无限递归栈溢出
return;
}
int mid = (lo + hi) / 2;
sort(a, aux, lo, mid);
sort(a, aux, mid + 1, hi);
merge(a, aux, lo, mid, hi);
}
private static void merge(Comparable[] a, Comparable[] aux, int lo, int mid, int hi) {
int i = lo, j = mid + 1;
for (int k = lo; k <= hi; k++) {
aux[k] = a[k];
}
for (int k = lo; k <= hi; k++) {
if (j > hi) {
a[k] = aux[i++];
} else if (i > mid || less(aux[j], aux[i])) {
a[k] = aux[j++];
} else {
a[k] = aux[i++];
}
}
}
public static void main(String[] args) {
Integer[] a = {4, 3, 5, 6, 9, 19, 23, 54, 75, 1, 88, 44, 45, 54, 78, 12, 14, 15, 16, 11, 991, 765, 28, 29, 49, 81, 80};
MergeSort.sort(a);
for (Integer i : a) {
StdOut.print(i + " ");
}
}
}
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