Design a function f, such that: f(f(n)) == -n Where n is a 32 bit signed integer; you can't use complex numbers arithmetic. If you can't design such a function for the whole range of numbers, design it for the largest range possible.

Two strings can be chained if the first one ends with the same character second one starts with. Given set of 'n' strings, how can we verify efficiently, whether they can be chained or not?

e.g. cat, dog, toad  answer is YES.
for    tape ate ass answer is NO.

Given an array of integers of size N, if M elements are removed from it the rest of the elements will be in sorted order. What is a good algorithm to find those M elements?