Is there an idiom or phrase which means:
The solution for the problem is the cause itself.
I was thinking of
Use the snake to suck out the venom
which, I'm unsure, is a valid phrase.
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Fighting fire with fire is an idiom meaning a response to an attack with a similar or equal attack (i.e. if someone fires a weapon at you, you fire a weapon at them).
In a negative context:
Set a thief to catch a thief Prov. The best person to catch a thief is another thief, because he or she knows how thieves think. The government set a thief to catch a thief, hiring a stockbroker convicted of fraudulent practices to entrap the stockbroker they were investigating for fraud.
I've never seen the term generalised this way, but you could describe the solution as homeopathic.