Find longest common subset between two sets
The algorithm to find Longest common subset relies on dynamic programming.
Given two sets - example:
X = <B,C,D,B>
Y = <A,B,C,B,D,A,B>
Check if set X is a subset of set Y, where X<1,m> and Y<1,n>
This algorithm requires to prepare a helper table using dynamic programming approach, which is later used in print_lcs function.