问我不确定我的分区函数出了什么问题
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Stack Overflow用户

提问于 2013-04-25 01:31:28

回答 1查看 179关注 0票数 0

Eclipse一直告诉我我的分区函数有问题。它是用java编写的，是一个关于数组排序的类的一部分。

分区是这样工作的:数组中有两个索引i和j，在分区算法的最开始，i指向数组中的第一个元素，j指向最后一个元素。然后，算法向前移动i，直到找到值大于或等于枢轴的元素。索引j向后移动，直到找到值小于或等于透视的元素。如果i≤j，那么它们被交换，并且i步到下一个位置(i + 1)，j步到前一个位置(j - 1)。当i大于j时，算法停止。

你能看到问题出在哪里吗，因为我很难找到它。如果您能帮上忙，我们将不胜感激。

public static int partition(int arr[], int left, int right)
    {
        int x = arr[right];

        int i = left-1;
        int temp=0;

        for (int j=left; j<right; j++)
        {
            if(arr[j]<=x)
            {
                i++;
                temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;

            }
        }

        temp = arr[i+1];
        arr[i+1] = arr[right];
        arr[right] = temp;
        return (i+1);

    }

编辑

Eclipse说有两个问题，一个是分区函数中的这行代码：

int x = arr[right];

使用我的测试类中的这一行：

sort.partition(array, 100, array.length);

下面是测试类，其中包含我没有提到的函数。

import java.util.Random;


public class test {

    /**
     * @param args
     */
    public static void main(String[] args) {

        int size = 1000;
        int max = 5000; 
        int[] array = new int[size];
        int loop = 0; 

        Random generator = new Random();
        //Write a loop that generates 1000 integers and 
        //store them in the array using generator.nextInt(max)

        generator.nextInt(max); //generating one

        //I need to generate 1000
        //So I need some kind of loop that will generate 1000 numbers. 

        for (int i =0; i<1000; i++)
        {
            generator.nextInt(max);
        }



        /**
         * After I do this, I'll have the array, array. 
         * Then comes what's under this. 
         * THat method is for measuring the time.
         * System.currentTimeMillis();, 
         * with this, I can collect a time for the start of the method
         * and one for the end. 
         * Time at the end, minus the time at the start
         * gets us the running time. 
         */



        long result;

        long startTime = System.currentTimeMillis();
        sort.quickSort(array,  100,  array.length-1);
        long endTime = System.currentTimeMillis();
        result = endTime-startTime; 

        System.out.println("The quick sort runtime is " + result + " miliseconds");

        long result2;

        long startTime2 = System.currentTimeMillis(); 
        sort.partition(array, 100, array.length);
        long endTime2 = System.currentTimeMillis();
        result2 =  endTime2 - startTime2;
        System.out.println("The partition runtime is "+result2 + " miliseconds");

        long result3;

        long startTime3 = System.currentTimeMillis();
        sort.bubbleSort(array, 100);
        long endTime3 = System.currentTimeMillis();
        result3 = endTime3-startTime3;
        System.out.println("The bubble sort runtime is "+result3 + " miliseconds");

        long result4;

        long startTime4 = System.currentTimeMillis();
        sort.selectionSort(array, 100); //change the second number to change
        //the size of an array. 
        long endTime4 = System.currentTimeMillis();
        result4 = endTime4-startTime4;
        System.out.println("The selection sort runtime is "+result4 + " miliseconds");



    }

}