Question

我的任务是对各种排序算法的不同运行时间进行基准测试。我能够运行所有算法。但是，在处理大型数组时遇到溢出问题。用于快速排序的递归可能太深，但我不确定如何简化它。任何帮助将非常感激。以下是我的构造函数示例和快速排序：

 /**
 * constructor for sorting
 */
Sorting(int size) 
{
    arraySize = size;
    theArray = new int[size];
}

/**
 * creates a random array
 */
public void generateRandomArray() 
{

    for (int i = 0; i < theArray.length; i++) {
        theArray[i] = (int)(Math.random());
    }

    itemsInArray = arraySize - 1;

}

/**
 * creates an array that is almost sorted
 */
public void almostSortedArray()
{

    for (int i=0; i <theArray.length; i++)
    {
        theArray[i] = i;
    }

    theArray[theArray.length/2] = (int)(Math.random());


    itemsInArray = arraySize -1;
}

 /**
 * quick sort
 */
public void quickSort(int left, int right) {

    int pivot = theArray[right/2];
    int pivotLocation = partitionArray(left, right, pivot);

    if (right - left <= 0)
        return;

    else {

        quickSort(left, pivotLocation - 1);
        quickSort(pivotLocation + 1, right);

    }

}

public int partitionArray(int left, int right, int pivot) {

    int leftPointer = left -1 ;
    int rightPointer = right;

    while (true) {

        while (theArray[++leftPointer] < pivot)
            ;

        while (rightPointer > 0 && theArray[--rightPointer] > pivot)
            ;

        if (leftPointer >= rightPointer) {

            break;

        } else {

            swapValues(leftPointer, rightPointer);

        }

    }

    swapValues(leftPointer, right);

    return leftPointer;

}


/**
 * Swaps higher value for 
 */
public void swapValues(int indexOne, int indexTwo) {

    int temp = theArray[indexOne];
    theArray[indexOne] = theArray[indexTwo];
    theArray[indexTwo] = temp;
}

Answer 1

使用long或BigInteger而不是int。溢出意味着数字大于int可以容纳。

Answer 2

是arrayIndexOutOfBound还是溢出？查看在while循环中递增leftpointer的代码。假设所有元素都小于pivot，那么你试图访问一个不存在的元素，你应该得到ArrayIndexOutOfBound。对于右指针也一样，你需要在while循环中放入break，如果指针到达右端则循环应该终止。

`public int partitionArray(int left, int right, int pivot) {
int leftPointer = left -1 ;
int rightPointer = right;

while (true) {

    while (theArray[++leftPointer] < pivot){
        if(leftPointer == rightPointer) break; // Here i think you got IndexOutOfBound
}
    while (rightPointer > 0 && theArray[--rightPointer] > pivot)
        if(rightPointer == LeftPointer) break;

    if (leftPointer >= rightPointer) {

        break;

    } else {

        swapValues(leftPointer, rightPointer);

    }

}

swapValues(leftPointer, right);`

快速排序溢出

2 个答案: