快速排序按降序排序而不是升序排序

Question

我刚刚实现了书中的快速排序算法并得到了奇怪的输出。它有效，但它按降序而不是升序排序。例如： [1, 5, 2, 10, 6, 9, 8, 3, 7, 4] 排序 [10, 9, 8, 7, 6, 5, 4, 3, 2, 1] 似乎不能在我的代码中找到源代码：

private void quicksort(int[] A, int p, int r) {
    if (p < r) {
        int q = partition(A, p, r);
        quicksort(A, p, q);
        quicksort(A, q + 1, r);
    }
}

private int partition(int[] A, int p, int r) {
    int x = A[p]; // pivot
    int i = p;
    int j = r;
    while (true) {

        while (A[i] > x) {
            i++;
        }

        while (A[j] < x) {
            j--;
        }
        if (i < j) {
            int temp = A[i];
            A[i] = A[j];
            A[j] = temp;
        } else {
            return j;
        }
    }
}

初次通话：

   quicksort(A, 0, A.length - 1);

如何计算快速排序的空间复杂度？

感谢你们

Answer 1

它在您的分区函数中，您按降序排序。

 while(true) {
 //ignore all the numbers greater than X to left
 while (A[i] > x) {
        i++;
    }
 //ignore all numbers lesser than X to right
 while (A[j] < x) {
        j--;
 }

 //swap a number lesser than X on left with a number greater than X on right
    if (i < j) {
        int temp = A[i];
        A[i] = A[j];
        A[j] = temp;
        i++;
        j--;
    } else {
        //Now the array is so sorted, that all numbers lesser than X are on right of it and greater than X are to left of it. Hence return position of X
        return j;
    }
 }

//对于升序：

 while(true) {

 while (A[i] < x) {
        i++;
 }

 while (A[j] > x) {
        j--;
 }

    if (i < j) {
        int temp = A[i];
        A[i] = A[j];
        A[j] = temp;
        i++;
        j--;
    } else {
        return j;
    }
}