Valon Software Engineer Interview Experience — Two-Hour Bank Service Build, Then an HM Round

Valon's onsite format is pretty unusual: you get 2 hours to implement one problem. The goal is to build a banking service made up of 5 parts. My feeling is that you need to get through at least parts 3-4, but you are not required to finish everything.

How the time is split:

First 30 minutes: go through the problem with an engineer, discuss the design, and start building.

Middle 90 minutes: you write the code on your own.

Last 30 minutes: another engineer joins the call, and you do a code walkthrough together, discussing your approach and the design decisions in it.

After the technical round there is also an HM interview, with the usual behavioral questions about teamwork, communication, leadership, etc.

Problem: every step comes with input/output.

Step 1: Build a BankService that support ATM transfers: View balance, deposit and withdraw cash

class ValonBankService:
    """ Code to be evaluated """
    def get_current_balance(...):
        pass
    def deposit_cash(...):
        pass
    def withdraw_cash(...):
        pass

class FileInterface:
    """ Used for debugging/testing purposes only
    We don't care about the code in this class, you can even hardcode the file paths if you'd like. """
    def perform_bank_actions():
        # reads in input file
        # calls ValonBankService functions
        pass
    def write_bank_statements():
        # calls ValonBankService functions
        # writes to output file (based on whatever step you're on)
        pass

FileInterface.perform_bank_actions()
FileInterface.write_bank_statements()

Sample output:

account amount
PEACH1111 $5.00
PEACH2222 $10.00
PEACH3333 $15.00

Step 2: Add support to display transactions per account. We want to track all transactions, even those that have failed. The columns are time, account, credit, debit, status, type, balance. Sample rows:

2020-08-01 1:00:00 | PEACH1111 | $10.00 | SUCCESS | ATM | $10.00
2020-08-01 7:00:00 | PEACH1111 | $5.00  | SUCCESS | ATM | $5.00
2020-08-01 5:00:00 | PEACH2222 | $20.00 | SUCCESS | ATM | $20.00
2020-08-01 6:00:00 | PEACH2222 | $25.00 | FAILED  | ATM | $20.00

Step 3: Create a function that transfers funds from one account to another

def instant_transfer(...):
    pass

2020-08-01 6:00:00 | PEACH1111 | $2.00 | SUCCESS | INSTANT TRANSFER | $7.00

Step 4: Support transfers to/from external bank, each external transfer will incur a fee

2020-08-01 7:00:00 | PEACH2222 | $5.00 | SUCCESS | INSTANT TRANSFER | $13.00
2020-08-01 7:00:00 | PEACH2222 | $0.01 | SUCCESS | FEE | $12.99

Step 5: Create a function to support slow fund transfers. Assume that once you initiate a slow transfer, the funds are no longer usable until they reach the ending bank account

2020-08-01 6:00:00 | PEACH1111 | $2.00 | SUCCESS | SLOW TRANSFER | $7.00