techinterviewArchiveRandom postSubscribeLog DateWelcome to techInterview, a site for technical interview questions, brain teasers, puzzles, quizzles (whatever the heck those are) and other things that make you think!SearchFebruary11,2011Text postGetting a fair result with an unfair coinHow can you get a fair coin toss if someone hands you a coin that is weighted to come up heads more often than tails?Notes: 41 notesJanuary5,2011Text postWe are NY Tech asks:"How many unique areas of human knowledge have the right size of passionate users to make it as a Stack Exchange site?”Answer: 30,000.Notes: 5 notesNovember29,2010Text postStoring 1 million phone numbersWhat is the most efficient way, memory-wise, to store 1 million phone numbers?  Apparently this is an interview question at Google, although this seems like its a bit too easy.Notes: 8 notesTags: google interviewApril16,2010Text postReverse a StringA typical programming interview question is “reverse a string, in place”. if you understand pointers, the solution is simple. even if you don’t, it can be accomplished using array indices. i usually ask candidates this question first, so they get the algorithm in their head. then i play dirty by asking them to reverse the string word by word, in place. for example if our string is “the house is blue”, the return value would be “blue is house the”. the words are reversed, but the letters are still in order (within the word).Read MoreNotes: 16 notesApril16,2010Text post
100 Doors in a Row
Problem: you have 100 doors in a row that are all initially closed. you make 100 passes by the doors starting with the first door every time. the first time through you visit every door and toggle the door (if the door is closed, you open it, if its open, you close it). the second time you only visit every 2nd door (door #2, #4, #6). the third time, every 3rd door (door #3, #6, #9), etc, until you only visit the 100th door.
question: what state are the doors in after the last pass? which are open which are closed?
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Notes: 34 notes
April
16,
2010
Text post
Red Marbles, Blue Marbles
Problem: you have two jars, 50 red marbles, 50 blue marbles. you need to place all the marbles into the jars such that when you blindly pick one marble out of one jar, you maximize the chances that it will be red. (when picking, you’ll first randomly pick a jar, and then randomly pick a marble out of that jar) you can arrange the marbles however you like, but each marble must be in a jar.
Solution
Chance! chance is easy if you know how to do the formula. we know that we have two choices to make. first we’ll pick a jar, and each jar will have a 1/2 chance of being picked. then we’ll pick a marble, and depending how we stack the marbles, we’ll have a (# of red marbles in jar)/(# of total marbles in jar) chance of getting a red one.
for example, say we put all the red marbles into jar A and all the blue ones into jar B. then our chances for picking a red on