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I saw a puzzle in a contest in Iran held by an association called "Rahneshan" and the original text of the contest is uploaded HERE and of course both website and text are in Persian.

Between "City A" and "City B", there is a big cable which contains 100 separate wires inside it. Unfortunately, the wires are knotted together and we can't tell which head of a wire in one side (City A), belongs to which tail on the other side (City B).

The only tools that we have are:

  • A power outlet
  • A test light (which can be used to determine if electricity is flowing through a wire)

We can make a round-trip from City A to City B and back once.

How can we determine which endpoints belong to which wires?

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    $\begingroup$ Is this a puzzle that your created yourself, or that you found elsewhere? If it is not original then please provide attribution. Puzzles without attribution may be closed. $\endgroup$
    – bobble
    Oct 18, 2020 at 20:48
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    $\begingroup$ An active contest? We have a policy against puzzles from active contests. $\endgroup$
    – bobble
    Oct 18, 2020 at 21:20
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    $\begingroup$ Please edit in attribution, then $\endgroup$
    – bobble
    Oct 18, 2020 at 21:25
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    $\begingroup$ To whoever closed it, this is not a duplicate. The alleged duplicate question asks "What is the fewest number of trips from one end of the cable to the other required to identify ...each individual wire." This question stipulates only ONE trip can be made. $\endgroup$
    – Earlien
    Oct 18, 2020 at 23:12
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    $\begingroup$ The answers to the linked question are answers to this question as well. They lay out a strategy, requiring one round-trip, that can solve the problem. Since the answers are the same the focus on a different part of the solution does not matter. $\endgroup$
    – bobble
    Oct 19, 2020 at 3:09

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