There are nine coins, one of which is counterfeit. How many times can you find it from the balance? How to weigh?

Divide nine coins into three parts, each with three coins, marked as A, B and C. ..

First time: say a and b.

(1) If they are the same, the counterfeit money is in C. The second time: say C 1 and C2, if they are the same, the counterfeit money is C3; If not (assuming the weight of C 1), call C 1 and C3 for the third time; If they are the same, C2 is forged; If not, C 1 is counterfeit money.

(2) If they are different (one weight), the second call: A 1B 1 and A2B2 are the same, it is called the third call: A3 and C1; If they are the same, the counterfeit money is B3; If not, the counterfeit money is A3.

If A 1B 1 is different from A2B2 (A 1B 1 weight), it is called the third time: A 1 and C 1. If they are the same, the counterfeit money is B2; If not, counterfeit money is A 1. If A 1B 1 and A2B2 are different (A2B2 is heavy), it is called the third time: A2 and c1; If they are the same, the counterfeit currency is b1; If not, the counterfeit money is A2.