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Quick Summary
Process accounts sequentially to identify those that conflict with previously successful registrations.
Rejected accounts do not update the pool of claimed contact information.
Return the zero-based indices of all duplicate accounts in ascending order.
What This Tests
Efficient membership testing using hash sets
Sequential state tracking across parallel input streams
Conditional branching based on accumulated history
Optimizing lookup and insertion operations for linear time complexity
Common Patterns
Hashing
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