最小的K个数：用快排的思想去解相关问题

int Partition(int data[], int length, int start, int end)
{
    if(data == NULL || length <= 0 || start < 0 || end >= length)
        throw new std::exception("Invalid Parameters");
    
    int index = RandomInRange(start, end);
    swap(&data[index], &data[end]);
    
    int small = start - 1;
    for(index = start; index < end; ++index)
    {
        if(data[index] < data[end])
        {
            ++small;
            if(small != index)
                swap(&data[index], &data[small]);
        }
    }
    
    ++small;
    swap(&data[small], &data[end]);
    
    return small;
}

void GetLeastNumbers(int *input, int n, int *output, int k)
{
    if(input == NULL || output == NULL || k > n || n <= 0 || k <= 0)
        return;
    
    int start = 0;
    int end = n - 1;
    int index = Partition(input, n, start, end);
    while(index != k - 1)
    {
        if(index > k - 1)
        {
            end = index - 1;
            index = Partition(input, n, start, end);
        }
        else
        {
            start = index + 1;
            index = Partition(input, n, start, end);
        }
    }
    
    for(int i = 0; i < k; ++i)
        output[i] = input[i];
}