Algorithm · Airbnb · Hard
Consider a sign-up flow where each user submits a name, email, and phone number. The system processes submissions one by one in the given order. For a submission to be accepted, both its email and its phone must be unique among all previously accepted submissions. If either the email or the phone has already been used by a prior accepted account, the submission is rejected as a duplicate. Rejected submissions do not consume the email or phone; they remain available for…
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