If we are given "c{a}{b}" and the map as inputs, then we can simply check for the existence if keys {a} and {b} in the map and if both exists, then use StringBuilder to build out the key as- c.append(map.get(a)).append(map.get(b)). If this new key combination exists in the map, return the value, else we fall out of the if statements to return null or -1.

There's a lot of elements to typically cover in these questions, clarifications, scoping, making sure you're answering the actual question the interviewer is looking for you to answer, etc. Could be worth doing a mock interview with one of the Prepfully PayPal Senior Software Engineer experts... they've worked in the role so they clearly know how to get through the interview. prepfully.com/practice-interviews