sort.java

来自「一个java实现的R树」· Java 代码 · 共 62 行

package rtree;

/**
 * Static class used for providing static methods for sorting arrays of Objects, using
 * comparators. It is needed for jdk 1.1 compatibility.
 * <p>
 * Created: Fri Jul 02 18:42:36 1999
 * <p>
 * @author Hadjieleftheriou Marios
 * @version 1.0
 */
public class Sort  {
    
    private Sort() {
    }
    
    private static void mergeSort(Object src[], Object dest[],
				  int low, int high, Comparator c) {
	int length = high - low;

	// Insertion sort on smallest arrays
	if (length < 7) {
	    for (int i=low; i<high; i++)
		for (int j=i; j>low && c.compare(dest[j-1], dest[j])>0; j--)
		    swap(dest, j, j-1);
	    return;
	}

        // Recursively sort halves of dest into src
        int mid = (low + high)/2;
        mergeSort(dest, src, low, mid, c);
        mergeSort(dest, src, mid, high, c);

        // If list is already sorted, just copy from src to dest.  This is an
        // optimization that results in faster sorts for nearly ordered lists.
        if (c.compare(src[mid-1], src[mid]) <= 0) {
           System.arraycopy(src, low, dest, low, length);
           return;
        }

        // Merge sorted halves (now in src) into dest
        for(int i = low, p = low, q = mid; i < high; i++) {
            if (q>=high || p<mid && c.compare(src[p], src[q]) <= 0)
                dest[i] = src[p++];
            else
                dest[i] = src[q++];
        }
    }

    private static void swap(Object x[], int a, int b) {
	Object t = x[a];
	x[a] = x[b];
	x[b] = t;
    }

    public static void mergeSort(Object[] a, Comparator c) {
        Object aux[] = (Object[])a.clone();
        mergeSort(aux, a, 0, a.length, c);
    }
    
} // Sort