快速排序

[ContextMenu("Test")]
void Test()
{
    var array = new int[] { 13, 34, 1, 5, 21, 3, 2, 8, 1 };
    Quick_Sort(array);

    Debug.Log("Final: " + string.Join(",", array.Select(m => m.ToString()).ToArray()));
}

void Quick_Sort(int[] array)
{
    Quick_Sort(array, 0, array.Length - 1);
}

void Quick_Sort(int[] array, int leftIndex, int rightIndex)
{
    if (rightIndex - leftIndex < 2) return;

    var key = leftIndex + ((rightIndex - leftIndex) / 2);
    var direction = -1;
    var flag = 0;

    while (true)
    {
        if (direction == -1)
        {
            for (int i = leftIndex; i <= key; i++)
            {
                if (array[i] > array[key])
                {
                    Swap(array, i, key);
                    key = i;
                    flag = -1;
                    break;
                }
            }
        }
        else
        {
            for (int i = key + 1; i <= rightIndex; i++)
            {
                if (array[key] > array[i])
                {
                    Swap(array, i, key);
                    key = i;
                    flag = -1;
                    break;
                }
            }
        }

        direction *= -1;
        flag++;

        //左右两边都没有的情况
        if (flag == 2)
        {
            //再拆分成两个子序列进行排序
            Quick_Sort(array, 0, key);
            Quick_Sort(array, key + 1, rightIndex);
            break;
        }
    }
}

void Swap(int[] array, int x, int y)
{
    var tmp = array[x];
    array[x] = array[y];
    array[y] = tmp;
}