*createNumbers: 

-> check if len is greater than 2
-> create new array numbers, use malloc and check if correct
-> set seed for rand()
-> create new TreeNode root
-> add new value to tree using addToTree and rand()
-> addToTree sets isDup to 1, if value already exists
-> if value does not already exist -> add to numbers[]
-> 


getDublicate:

-> numbers (Zeiger != NULL) und len (min. 2) check
-> define new array numbersCopy
-> copy numbers to numbersCopy 
    -> simple loop to copy each element number -> numbersCopy
-> sort numbersCopy with qsort
-> compare each element of numbersCopy with next element (if numbersCopy[i] == numbersCopy[i+1] -> dublicate was found, because same values are right next to each other)
-> return found dublicate

compare:

-> gibt 1 aus, wenn a größer ist
-> gibt -1 aus, wenn b größer ist
-> gibt 0 aus wenn a==b
