Interview Puzzles :: Discussion

Sahil has got a challenging problem from his friend Akhil. Sahil has to find all values of n for which one can fill an n × n table with +’s and -’s (one per cell) so that every cell has exactly one neighbor with the opposite sign. Two cells are considered neighbors if they are either in the same row or the same column. Can you help out Sahil to find such values of n?