CareerCup

Example given in question is wrong. Please rectify that to avoid any confusion.

1+0==1
but -11 +1 +12 !=1

This problem mainly deals with the storage of fraud credit cards. System should return whether the credit card details provided are proper or fraud in optimum time.

So, efficient storing the list of fraud cards includes
a.) Use optimum space.
b.) Check if credit card is already present in list or not in minimal time
c.) Insert new list of credit cards to the existing storage
d.) Deleting existing card from storage if required

Once we get the information whether the credit card is fine or fraud, we can proceed further as per requirement.

To solve the storage problem in our system, we can use hash table . but in this case, we need to design a good hash function.
Alternatively, we can use trie as well to store the credit card info