Quant, Math & Computer Science Puzzles for Interview Preparation & Brain Teasing
A collection of ~225 Puzzles with Solutions (classified by difficulty and topic)

Jul 11, 2014

3D Tic Tac Toe Puzzle

Source: Shared by Alok Mittal (Cannan Partners)

Problem:
A 3x3 tic tac toe has 8 "winning lines" (3 horizontal, 3 vertical and 2 diagonals). How many "winning lines" does the 3x3x3 3D tictactoe have? There is a brute force solution, and then there is the aha! solution.

Update (23 Oct 2014)
Solution: Posted in comments by Anti, Taz, Javier, Shubham Gupta, Leela. Detailed solution and much more advanced problems in the document http://library.msri.org/books/Book42/files/golomb.pdf


Jul 3, 2014

Mad Robot Puzzle

Source: http://nrich.maths.org/

Problem:




A mad robot sets off towards the North East on a journey from the point (0,0) in a coordinate system. It travels in stages by moving forward and then rotating on the spot. It follows these pseudo-code instructions:

SUB JOURNEY
    DISTANCE = 1000
    WHILE (DISTANCE > 0.001)
        MOVE DISTANCE
        STOP
        ROTATE(90, DEGREES, CLOCKWISE)
        DISTANCE = DISTANCE / 2
    END WHILE
    EXPLODE
END SUB

Where does the robot explode?

Update (23 Oct 2014):
Solution: Posted by me (Pratik Poddar) in comments!


Jul 1, 2014

Social Network Friendship Paradox

Problem / Observation:

The friendship paradox is the phenomenon first observed by the sociologist Scott L. Feld in 1991 that most people have fewer friends than their friends have, on average. Prove it mathematically.


Update (23 Oct 2014):
Solution: Posted by Mike Earnest and Taz in comments!