Directory listing

Makefile
combin.c
combin2.c with memoization (dynamic programming, Bellman's principle)
main.c
combin3.cpp (using std:map<std:pair<int,int>, long int> for memoization)
combin4.cpp (using std:map<std:tuple<int,int>, uint64_t> for memoization)
main4.cpp (using uint64_t type for combinations)