Saturday, March 31, 2012

magic square

You have a 3x3 square, fill with integers such that the sum for each row, for each column and in diagonal is 15. All the numbers must be different.

Hint: brute force is difficult (how many?), what would be number you put in the middle?

Friday, March 30, 2012

Table of reals

Given a table of real numbers of size mxn, is there an algorithm for making all the column sums and all the row sums positive? The only operation allowed is to change the sign of all the numbers in a column or in a row (one or more times).

Thursday, March 29, 2012


In a group of persons, a celebrity is know by everyone and all the other people are known by none. Detect all the celebreties

Wednesday, March 28, 2012

Monday, March 26, 2012

A classical one: reduced size and put into a bladder

This is one of those classical interview questions that are supposed to probe your creativity. i don't like those problems, if you want to test creativity just present some really hard problem you are trying to solve and perhaps you can be surprised by a new approach.

Anyway, suppose that you are reduced by 90% but still retaining your mass (what a sci-fi situation?) and you are put in a bladder (really?). What can you to do to safe your life?

Sunday, March 25, 2012

Ads -- betting on a query

You are a search engine which is selling ads for the query Q and your current valuation is 100$. Your competitor  has similar search performance but it's selling at 40$. What will you do?

Saturday, March 24, 2012

Given N horses, how many races do you need?

Given N horses, how many races do you need to identify top 3 horses. Assume that a race cannot have more than 5 horse together.

Given N horses, how many races do you need?

Given N horses, how many races do you need to identify top 3 horses. Assume that a race cannot have more than 5 horse together.

Friday, March 23, 2012

You have 25 bits

Every time you turn a bit on, you should put it as far away as possible from the the other bit already turned on. What is the best bit to turn on at the beginning?

Thursday, March 22, 2012

D'oh: Facebook Buys 750 IBM Patents For Defense

Facebook is purchasing 750 patents from IBM in order to bolster defenses against patent infringement suits, especially the one filed by Yahoo.

Tuesday, March 20, 2012

Saturday, March 17, 2012

IP to Countries

Write a function that will return a two character string representing a country code given an IP address as its input. Can this be made in memory?

Friday, March 16, 2012

a classical problem: coin change

Given a value in money N, and we want to change N into coins extracted from a set S={S1, ... Sm} of different coin values. How many diffferent ways to do we have to make the change. Assume that there are infinite coins of type Si.


Define C(S, N, M) the way of changing the N given the M coins in S and compute the recursive solution

Sunday, March 4, 2012

Why people are not using LinkedIn for Search? my opinion: their ranking is broken

Read an article about LinkedIn where the founder was complaining about people who are not using LinkedIn for searching new talents.  He says: "I have a frustration that people don't understand it. I had a CEO at one of my portfolio companies say to me, 'How do I use LinkedIn to find a CFO?' I said, 'Well have you tried typing "CFO" into the search box?' It's flabbergasting"

Perhaps, this is because the ranking system and the recommendation system in Linkedin are both fundamentally broken. Everyone can write whatever she likes in her CV and she can collude with other members for increasing the number of external references. There is no control and no sound ranking system in place. In short, anyone can inflate the value of her own LinkedIn profile.

Now why this is happening? Linkedin ranks users just using on their distance from my position in the social graph. Also, they consider textual match as a ranking feature. In my view, this is indeed a very primitive form of ranking and they should start investigating the idea of assigning credits to users. In this model, you spend a credit whenever you endorse a user and you gain credit when your endorsement was judged as positive by other users. This is a model used in real world where you spend some part of your social credit when you endorse someone. Plus, you earn some money when your endorsement will become a new hire.

So, Just a little feature suggestion for my friends in LinkedIn.

Saturday, March 3, 2012

Social reverse dating

Ok, now I saw everything in social. Social reverse dating is outrageous ;)

Friday, March 2, 2012

Money related startups -- An overview

I am started to be interested into systems for transferring money in Internet. Here an overview of the most interesting technologies and startups

  • Bitcoin for moving money with safe transactions
  • Transferwise, move money in different currencies with very low commissions
  • Square, pay with your credit card using your mobile phone
  • Boku, charge your mobile bill and get an sms for confirming the transaction
  • Monitise, use your mobile as a bank
This was my posting for turning Skype into a cash cow for mobile payments and facilitate money transfer using your own Skype account.