在字符串数组上使用quicksort

Question

我是一名编程学生,而不是发布整个作业,我只是要求帮助解决我已经尝试了几个小时才能理解的内容.我的任务是使用quicksort方法对字符串数组进行排序.作为这个问题的一部分,我所做的其他任务都很好但是当我通过打印字符串数组测试排序方法时,它完全混乱,没有任何看似押韵或理由.请帮助我查明代码中的错误,或者我忽略的几个明显的错误.提供的字符串数组是65个名称的列表:http://pastebin.com/jRrgeV1E,方法的代码如下:

private static void quickSort(String[] a, int start, int end)
{
        // index for the "left-to-right scan"
        int i = start;
        // index for the "right-to-left scan"
        int j = end;

        // only examine arrays of 2 or more elements.
        if (j - i >= 1)
        {
            // The pivot point of the sort method is arbitrarily set to the first element int the array.
            String pivot = a[i];
            // only scan between the two indexes, until they meet.
            while (j > i)
            {
                // from the left, if the current element is lexicographically less than the (original)
                // first element in the String array, move on. Stop advancing the counter when we reach
                // the right or an element that is lexicographically greater than the pivot String.
                while (a[i].compareTo(pivot) < 0 && i <= end && j > i){
                    i++;
                }
                // from the right, if the current element is lexicographically greater than the (original)
                // first element in the String array, move on. Stop advancing the counter when we reach
                // the left or an element that is lexicographically less than the pivot String.
                while (a[j].compareTo(pivot) > 0 && j >= start && j >= i){
                    j--;
                }
                // check the two elements in the center, the last comparison before the scans cross.
                if (j > i)
                    swap(a, i, j);
            }
            // At this point, the two scans have crossed each other in the center of the array and stop.
            // The left partition and right partition contain the right groups of numbers but are not
            // sorted themselves. The following recursive code sorts the left and right partitions.

            // Swap the pivot point with the last element of the left partition.
            swap(a, start, j);
            // sort left partition
            quickSort(a, start, j - 1);
            // sort right partition
            quickSort(a, j + 1, end);
        }
    }
    /**
     * This method facilitates the quickSort method's need to swap two elements, Towers of Hanoi style.
     */
    private static void swap(String[] a, int i, int j)
    {
    String temp = a[i];
    a[i] = a[j];
    a[j] = temp;
    }

Answer 1

好吧,我错了,它会起作用,发现你的小错误.

看看wikipedias伪代码

您会注意到while循环中的条件导致错误

如果你改变(a[i].compareTo(pivot) < 0 && i <= end && j > i)和(a[j].compareTo(pivot) > 0 && j >= start && j >= i)对

(a[i].compareTo(pivot) <= 0 && i < end && j > i)和(a[j].compareTo(pivot) >= 0 && j > start && j >= i).