tungwaiyip.info

home

about me

links

Blog

< July 2010 >
SuMoTuWeThFrSa
     1 2 3
4 5 6 7 8 910
11121314151617
18192021222324
25262728293031

past articles »

Click for San Francisco, California Forecast

San Francisco, USA

 

Find Sophie Solution (Facebook Programming Puzzle)

This is the fourth and probably my last post about solving Facebook programming puzzle. The Find Sophie problem is a buffet (hardest) level puzzle. It is basically a variation of the traveling salesman problem. Traveling salesman is of course, a NP-complete problem. But before you throw up your hand, consider the puzzle refers to locations in your home where you may find a cat. Just how many locations are there. Let's say living room, dining room, bedroom, on the bed, under the desk, behind the curtain, ... etc. If Facebook is not very wicked, this puzzle should be bounded to a low hundreds of locations. This mean it is still possible to solve using some relatively simple search algorithm.

Here is the outline of my solution:

  1. Prepare to enumerate all paths.
  2. Prefer the local optimal during the search. Remember the best solution encountered so far.
  3. Prune the search tree. For example if the current best solution has a score of 50. When you are considering another path, as soon as its score exceed 50, you should abandon it.
  4. Improve the pruning by taking the additional score to complete the path into account. For example, if the current score of a partial path is S, the minimum score to complete the remaining walk is Rmin. Then if S+Rmin > best score, prune it.

Actually I have submitted the solution a few months ago. Only today do I find out I have not posted my solution in my blog. So I'm really speaking from my memory. I hope my plan is still accurate. Again my un-tidied code is available.

The other 3 facebook puzzles I have solved was posted below:

2010.07.22 [] - comments

 

Highway Network

Have you wonder why a highway is designed like this? Let's say you are driving from a large city A to a large city B. Between them is a mid size city K. Now city A and B are major economic center and travel destinations. City K is none of that. It is yet another non-descript city. Everyone seems to heading to city B. There seems little reason for anyone to stop in city K.

Highway Design 1

The traffic on the highway was free flowing. Yet as you approach city K, local traffic starts to fill up the highways. the It gets to a point when everything comes to a crawl. You curse at the traffic. Then you wonder why must the intercity highway go through city K at all? Why doesn't it just bypass it so that travelers between A and B can have a smoother trip?

Highway Design 2

I have wondered about this for a long time. Now I have a theory. Roads are built for people. Where there are more people traveling, more investment will be made to build roads. This should make pretty good sense.

Now which kind of traffic have higher volume? Intercity traffic between A and B or local traffic in K? Despite your intuition that everyone seems to travel between A and B, there are actually more local traffic in city K. This is demonstrated by the fact that traffic is free flowing between A and B but clogged within city K. Therefore more funding will be allocated to build roads for residents of city K and not a bypass. Since intercity travelers are the minority, they will not be better off than the local residents of city K.

2010.07.10 [, ] - comments

 

past articles »

 

BBC News

 

Salman Rushdie stabbing suspect charged with attempted murder (13 Aug 2022)

 

Who is Salman Rushdie? The writer who emerged from hiding (13 Aug 2022)

 

Ukraine says it has taken out vital bridge in occupied Kherson (13 Aug 2022)

 

Taliban break up rare protest by Afghan women in Kabul (13 Aug 2022)

 

Medusa festival: High speeds winds cut Spanish festival short (13 Aug 2022)

 

Climate activists fill golf holes with cement after water ban exemption (13 Aug 2022)

 

Trump search warrant: FBI took top secret files from Mar-a-Lago (13 Aug 2022)

 

Climate change: Drought highlights dangers for electricity supplies (13 Aug 2022)

 

Southern Baptist abuse claims under DoJ investigation (13 Aug 2022)

 

Kenya elections 2022: Raila Odinga and William Ruto in tight presidential race (13 Aug 2022)

more »

 

SF Gate

 

These were the highest-paying Silicon Valley tech companies in 2021 (19 Jul 2022)

 

'This will be somewhat painful': Elon Musk talks Twitter takeover in extended interview at TED2022 Vancouver (14 Apr 2022)

 

Best Background Check Services in 2022, Top 13 People Finder Sites Reviewed (5 Apr 2022)

 

Better.com employees got severance checks before they were laid off (9 Mar 2022)

 

Apple joins other Bay Area tech giants in responding to Russian invasion of Ukraine (1 Mar 2022)

 

Uber will now show you how you’re rated by drivers (18 Feb 2022)

more »


Site feed Updated: 2022-Aug-13 15:00