Information Storage and Retrieval

1. Decode the following Variable Byte encoded string : 
   10000101 10001111 11011111 00000111 11000101 00000001 11111110
   
   
2. Encode the following postings list using Variable byte Encoding : 
   2, 8, 20, 186, 258, 1032
   
   
3. Decode the following Gamma encoded string : 
   11000110001110100111100110111011011111111001000100
   
   
4. Gamma Encode the following postings list : 
   1,25,36,129,130,132,525

note:

After reviewing several of the quiz submissions, I noticed a pattern of misunderstanding that I wanted to address. I also went back to the posted slides and I noticed a very subtle error in the gamma code example slide that is itself a reflection of this misunderstanding. 

In the gamma code example slide, The intention was to reference two numeric values that were being encoded, but I specifically called them "docIDs". Based on the process for how we generate a postings list from docIDs, the Postings list below that table is then inherently incorrect!

The gamma code for 13 is 1110,101 and the gamma code for 25 is 11110,1001. If these are both Document IDs rather than simple numeric values being encoded, then the Postings list should be: 

11101011110100 NOT 1110101111101001

The rationale for this was something that was spoken to specifically in the lecture, but I did not explicitly call it out in that example in the slides. Based on the number of responses that are missing this key concept -  and because I feel it's more important for you to understand the idea rather than to strip away points - If you wish to ponder this and amend your submission you may do so!  

This key rule for how we build postings lists applies to both Variable Byte encoding as well as Gamma codes!