快速排序算法的实现

void change_integer(int *p1, int *p2)
{
    int tmp = *p1;
    *p1 = *p2;
    *p2 = tmp;
}

int partion(int arr[], int length, int start, int end)
{
    int index = rand()%(end-start+1) + start;
    change_integer(arr+index, arr+end);
    int small_pos = start-1;
    for(int i=start; i<end; ++i)
    {
        if(arr[i] < arr[end])
        {
            ++small_pos;
            change_integer(arr+small_pos, arr+i);
        }
    }
    ++small_pos;
    change_integer(arr+small_pos, arr+end);
    return small_pos;
}

void quick_sort(int a[], int length, int start, int end)
{
    if(start == end)
        return ;
    int index = partion(a, length, start, end);
    if(index > start)
    {
        quick_sort(a, length, start, index-1);
    }
    if(index < end)
    {
        quick_sort(a, length, index+1, end);
    }
}