Imagine you are a government official with confidential messages to send. But spies want to intercept the messages. To tap a certain microwave link, your opponents must be in the line of sight of the transmitter. This positioning puts them in danger of detection and arrest, so you are sure they will attempt the job only once and for no more than 10 minutes. The trouble is, you don't know which 10-minute intervals they will choose.

You have seven messages, labeled alphabetically, to send in as short a time as possible. Their lengths are:

This article was originally published with the title Short Taps.

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