CareerCup

Take two pointers, read and write.
Read points to the next read index
Write points to the next write index

class Ring
{
    string buffer;
    int n, r, w;    // size of ring buffer, read pointer, write pointer

public:

    Ring(int _n) : n(_n)
    {   r = w = 0;  }

    string Read(size_t sz)
    {
        string chunk;

        while (r != w && chunk.length() < sz)
        {
            chunk += buffer[r++];

            if (r == n)
                r = 0;
        }

        return chunk;
    }

    size_t Write(string chunk)
    {
        int i;

        for (i=0; i<chunk.length(); i++)
        {
            if ((w+1) % n == r)
                break;

            buffer[w++] = chunk[i];
            
            if  (w==n)
                w = 0;
        }
        
        return i;
    }
};

class RingBuffer {
	public:
		RingBuffer(int size)
		{
			if (size > 0) {
				// adjust size to support the read/write pointers overflow
				int pow = 0;
				while (size != 0) {
					++pow;
					size >>= 1;
				}
				size = 1 << pow;

				data_.resize(size);
			}
			w_ = r_ = 0;
		}
		int Write(vector<int> const &block)
		{
			int written_count = min(block.size(), data_.size() - (w_ - r_));
			for (int i = 0; i < written_count; ++i) {
				data_[w_++ % data_.size()] = block[i];
			}
			return written_count;
		}
		int Read(int count, vector<int> &out)
		{
			out.clear();
			int read_count = count > 0 ? min(count, w_ - r_) : 0;
			for (int i = 0; i < read_count; ++i) {
				out.push_back(data_[r_++ % data_.size()]);
			}
			return read_count;
		}

	private:
		int w_, r_;
		vector<int> data_;
};