The quickSort1.java Program
// quickSort1.java
// demonstrates simple version of quick sort
// to run this program: C>java QuickSort1App
////////////////////////////////////////////////////////////////
class ArrayIns
{
private double[] theArray; // ref to array theArray
private int nElems; // number of data items
//-------------------------------------------------------------
public ArrayIns(int max) // constructor
{
theArray = new double[max]; // create the array
nElems = 0; // no items yet
}
//-------------------------------------------------------------
public void insert(double value) // put element into array
{
theArray[nElems] = value; // insert it
nElems++; // increment size
}
//-------------------------------------------------------------
public void display() // displays array contents
{
System.out.print("A=");
for(int j=0; j<nElems; j++) // for each element,
System.out.print(theArray[j] + " "); // display it
System.out.println("");
}
//-------------------------------------------------------------
public void quickSort()
{
recQuickSort(0, nElems-1);
}
//-------------------------------------------------------------
public void recQuickSort(int left, int right)
{
if(right-left <= 0) // if size <= 1,
return; // already sorted
else // size is 2 or larger
{
/*
這裏是用於比較的數的取值。它必須從要進行排序的序列或其子序列中取值，因爲這樣做才能保證劃分與比較有效。
*/
double pivot = theArray[right]; // rightmost item
// partition range
int partition = partitionIt(left, right, pivot);
recQuickSort(left, partition-1); // sort left side
recQuickSort(partition+1, right); // sort right side
}
} // end recQuickSort()
//-------------------------------------------------------------
public int partitionIt(int left, int right, double pivot)
{
int leftPtr = left-1; // left (after ++)
int rightPtr = right; // right-1 (after --) *********** not right + 1
while(true)
{ // find bigger item
/*
這裏無須進行越界判斷，因爲pivot是取自序列 的最右邊。
*/
while(theArray[++leftPtr] < pivot)
; // (nop)
// find smaller item
/*
這裏必須進行越界判斷。
*/
while(rightPtr > leftPtr && theArray[--rightPtr] > pivot)
; // (nop)
if(leftPtr >= rightPtr) // if pointers cross,
break; // partition done
else // not crossed, so
swap(leftPtr, rightPtr); // swap elements
} // end while(true)
swap(leftPtr, right); //**************** put the pivot to the right place
return leftPtr; // return pivot location
} // end partitionIt()
//-------------------------------------------------------------
public void swap(int dex1, int dex2) // swap two elements
{
double temp = theArray[dex1]; // A into temp
theArray[dex1] = theArray[dex2]; // B into A
theArray[dex2] = temp; // temp into B
} // end swap(
//-------------------------------------------------------------
} // end class ArrayIns
////////////////////////////////////////////////////////////////
class QuickSort1App
{
public static void main(String[] args)
{
int maxSize = 16; // array size
ArrayIns arr;
arr = new ArrayIns(maxSize); // create array
for(int j=0; j<maxSize; j++) // fill array with
{ // random numbers
double n = (int)(java.lang.Math.random()*99);
arr.insert(n);
}
arr.display(); // display items
arr.quickSort(); // quicksort them
arr.display(); // display them again
} // end main()
} // end class QuickSort1App