h2. Additional problems
# Friend of a friend(interview question): Given two user names in a social network find design an efficient way to test if one is a friend of a friend of the other.

# Equal partition: Given a set A of 40 real numbers, find out if there is any way to split A in two sets such that the sums of their elements are equal. ($O(2^n/2$)$)
# Minimal vertex cover: Given a graph of n nodes (n <= 30), find out a set with the smallest number of vertices such that each edge in the  graph has at least one node inside the set. ($O(3^n/2^)$)

# Equal partition: Given a set A of 40 real numbers, find out if there is any way to split A in two sets such that the sums of their elements are equal. (Hint: complexity $O(2^n/2$)$)
# Minimal vertex cover: Given a graph of n nodes (n <= 30), find out a set with the smallest number of vertices such that each edge in the  graph has at least one node inside the set. (Hint: complexity $O(3^n/2^)$)

# Square: You're given an array L which represents the sizes of n planks. You have to answer if there's any way to form a square using the planks without breaking them of overlapping them. (Hint: complexity $O(4^n/2^)$)
# 8 puzzle: Solve 8 puzzle. (Hint: Each position is solvable in at most 31 moves.)