15-110 PS11 Sample Solutions - Spring 2018

1. 

(a) Routing of packets from one router to another or 
from a router to a destination computer.

(b) Breaking a message into packets with index numbers, 
sending and receiving acknowledgements, resending 
missing or corrupted packets (error checking). 

(c) Since TCP is designed to get all packets to the 
destination and resends when packets are dropped, 
video would stall as packets go missing.

2. 

(a) 255. Each value represents an 8-bit unsigned integer,
and 255 is the maximum 8-bit unsigned integer.

(b) 128 as an 8-bit unsigned value is 10000000.
Since this starts with 10, this is a class B address.

3.

(a) MYHEARTISINTHEWORK

(b) UWKUWTZFXITWSBJZPNFBZB

(c) ALLEGHENYMONOGAHELAOHIO (the three rivers of Pittsburgh)

4. 

(a) n = 47 * 151 = 7097
    r = 46 * 150 = 6900
    e = 7  (e and r are relatively prime)
    d = 3943  ((e*d)%r == 1)

(b) (4117 ** 7) % 7097 = 1145

(c) (1145 ** 3943) % 7097 = 4117

5.

(a) Watson uses concurrency by searching concurrently through many algorithms
    to trace down many possible answers for a Jeopardy clue,
    looking for evidence of these answers in its knowledge base, scoring
    each one based on how confident the algorithm is on the answer's
    correctness.

(b)
 1. Processes the question into parts of speech to help determine what
    the question may be asking.
 2. Hypothesis generation - determines all the possible things that the
    question may be asking about and gathers initial evidence
 3. Hypothesis rating - rates each piece of evidence by its relevancy
    or other heuristic to determine whether it can be used to support some
    answer/used against it
 4. Final rating and scoring - takes all the hypothesis left, rates
    them against past experience and other heuristics to determine a
    confidence level.  Whether Watson buzzes in is determined based on
    current standing and the calculated confidence

(c) The sentence uses the words "fly" and "bow" in different contexts.
    Examples: 
    fly: insect or verb (a plane can fly)
    bow: a violin bow, a big red bow, the bow of a boat

(d) A corpus requires a human intervention to discard anything that is
    out of date, poorly reguarded, or immaterial to the problem domain.
    This whole process is also known as curating.

6.

(a) P(A) = 0.5
    P(B) = 0.25
    P(B|A) = 0.4  (be careful: the probability of B _GIVEN_ A)
    P(A|B) = 0.5*0.4/0.25 = 0.8

(b) It might blend in to the background, it might have an odd shape 
    given the robot's perspective, it may be hard to determine its 
    shape (edge) given lighting, etc.

(c) 25
    (At the first turn, it can be 1*3 = 3 places.)
    (At the next turn, those 3 places turn into 3*3 = 9 places.)
    (At the next turn, those 9 places turn into 3*5 = 15 places.)
    (At the final turn, those 15 places turn into 5*5 = 25 places.)
    --- draw this out on graph paper to see this