Can you traverse an array? Do you know that a string is an array? Do you know how the end or length of a string is represented in your language of choise? Do you know how each character is represented? Do you understand Unicode? Do you understand memory allocation? Is the string being reversed in place or you allocating a new string? What are the space and performance trade-offs between those approaches? I mean, you can fill a whole interview with just this topic. So yes if your answer is string.reverse() then expect some follow-up questions.