refactoring c code assignment for b-tree into c++ code to use as my personal library
main concept is simillar with map in c++ standart library
API:
insert(std::pair(key, value))
same with insert in map
pop(key)
remove a node corresponding to key
if there is no node with that key, return false, else return true
find(key)
return pointer of the value corresponding to key
if there isn't, return nullptr
empty()
return either empty or not
size()
return number of nodes in tree
clear()
remove every nodes in tree