高级排序-快速排序-利用三数据取中划分的快速排序算法

package g_advancedSort.D_quickSort2;

/**

 * 利用三数据取中划分的快速排序算法

 * @author Administrator

 *

 */

public class QuickSortApp {
public static void main(String[] args) {
int maxSize = 16;
ArrayIns arr = new ArrayIns(maxSize);
for (int i = 0; i < maxSize; i++) {
long n = (int) (Math.random() * 199);
arr.insert(n);
}
arr.displays();
arr.quickSort();
arr.displays();
}

}package g_advancedSort.D_quickSort2;

public class ArrayIns {
private long arr[];
private int nElems;

public ArrayIns(int max) {
arr = new long[max];
nElems = 0;
}

public void insert(long value) {
arr[nElems++] = value;
}

public void displays() {
System.out.print("A = ");
for (int i = 0; i < nElems; i++) {
System.out.print(arr[i] + " ");
}
System.out.println();
}

public void quickSort() {
recQuickSort(0, nElems - 1);
}

/*
* 快速排序
*/
private void recQuickSort(int left, int right) {
int size = right - left + 1;
if (size <= 3)
manualSort(left, right);
else {
long median = medianOf(left, right);// 3数据项取中，并返回中间数字值,中间数字值对应的索引为right-1
int partition = partitionIt(left, right, median);// 返回中间索引
recQuickSort(left, partition);
recQuickSort(partition + 1, right);
}
}

/*
* 返回中间索引
*/
private int partitionIt(int left, int right, long pivot) {
int leftPtr = left;//
int rightPtr = right - 1;// pivot
while (true) {
while (arr[++leftPtr] < pivot)
;
while (arr[--rightPtr] > pivot)
;
if (leftPtr >= rightPtr)
break;
else
swap(leftPtr, rightPtr);
}
swap(leftPtr, right - 1);// pivot和leftPtr交换
return leftPtr;
}

/*
* 3数据项取中，并返回中间数字值
*/
private long medianOf(int left, int right) {
int center = (left + right) / 2;
if (arr[left] > arr[center])
swap(left, center);
if (arr[left] > arr[right])
swap(left, right);
if (arr[center] > arr[right])
swap(center, right);

swap(center, right - 1);
return arr[right - 1];
}

/*
* 针对数组个数<=3特殊情况所做出的操作
*/
private void manualSort(int left, int right) {
int size = right - left + 1;
if (1 == size) {
return;// break不了，又不想执行接下来的操作，所以return
} else if (2 == size) {
if (arr[left] > arr[right])
swap(left, right);
return;
} else {
if (arr[left] > arr[right - 1])
swap(left, right - 1);
if (arr[left] > arr[right])
swap(left, right);
if (arr[right - 1] > arr[right])
swap(right - 1, right);
}

}

/*
* 交换
*/
private void swap(int dex1, int dex2) {
long temp = arr[dex1];
arr[dex1] = arr[dex2];
arr[dex2] = temp;

}

}