Mask a card number
Support staff can see the last four digits of a card and nothing else.
- Every character except the last four becomes an asterisk.
- Anything four characters or shorter comes back untouched — there is nothing safe to hide.
maskCard(cardNo: string) → string
C++ needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
std::string maskCard(std::string cardNo) {
}Worked examples
| Call | Result |
|---|---|
maskCard(std::string("4506349012345678")) | std::string("************5678") |
maskCard(std::string("12345")) | std::string("*2345") |
maskCard(std::string("1234")) | std::string("1234") |
maskCard(std::string("")) | std::string("") |
Hint
Build the asterisks from the length, then glue on the tail.
Reference solution in C++
std::string maskCard(std::string cardNo) {
if (cardNo.size() <= 4) return cardNo;
return string(cardNo.size() - 4, '*') + cardNo.substr(cardNo.size() - 4);
}