QuickSort java implementation

Question

I am trying to implement the QuickSort algorithm but I am having trouble doing it. I think the problem is with the partitioning method where I make the first element of the array as the pivot and I use a pointer that puts all the smaller values to the left of the array, and lastly putting the pivot in the middle. Thank you.

My input is: {42,12,52,1,34,31,0,3} But I am getting: 12, 31, 1, 42, 0, 3, 52, 34

  public static void quickSort(int[] A) {
        quickSort(A, 0, A.length - 1);
    }

    private static int[] quickSort(int[] A, int low, int high) {
        if (low < high) { // if there is still at least 1 element left in the array
            int p = partition(A, low, high);
            quickSort(A, low, p - 1);
            quickSort(A, p + 1, high);
        }
        return A;
    }

    private static int partition(int[] A, int low, int high) {
        int pointer = low + 1;
        int temp = 0;

        for (int i = low + 1; i <= high; i++) {
            if (A[i] < A[low]) {    // if a num is less than pivot, then put to left
                temp = A[pointer];
                A[pointer] = A[i];
                A[i] = temp;
                pointer++;
            }
            temp = A[pointer - 1];
            A[pointer - 1] = A[low];
            A[low] = temp;
        }
        return pointer - 1;
    }

Answer 1

Oh I got it, I just need to put the part of the code where I place the pivot in the middle outside of the for loop.

Answer 2

Have int pointer = A[high] and add int i = (low - 1) where it is the index of the smaller element.

void quickSort(int[] A, int low, int high) {
    if (low < high) {
        int p = partition(A, low, high);

        quickSort(A, low, p - 1);
        quickSort(A, p + 1, high);
    }
}

int partition(int A[], int low, int high) {
    int pointer = A[high];
    int i = (low - 1);

    for (int j = low; j < high; j++) {
        if (A[j] <= pointer) {
            i++;

            int temp = A[i];
            A[i] = A[j];
            A[j] = temp;
        }
    }

    int temp = A[i + 1];
    A[i + 1] = A[high];
    A[high] = temp;

    return i + 1;
}