Revision 2a86aced-cc73-455d-bc12-fd733b09bbc4 - Code Golf Stack Exchange

# [Java (JDK)], 69 bytes

<!-- language-all: lang-java -->

 a->{int i=1,l=a.length,c=0;for(;a[i]!=2;c++)i=i*2%(l+~l%2);return c;}

[Try it online!][TIO-jt4ec5fa]

[Java (JDK)]: http://jdk.java.net/
[TIO-jt4ec5fa]: https://tio.run/##bZJPb6MwEMXv@RTTSkjQOCg2If9YIvWy0h56am9RDi4JqbPEIGwqRRH71bPPUEVJdw8IzbzfvGfGHOSnHB22vy/qWJW1pQPqsLGqCJ@SwT@9vNGZVaV2YlZIY@hFKk3nAVHVvBcqI2OlxeuzVFs6QvNfba30fr0hWe9N0KFEb@UvbX9@mf1Q2q43K8opvcjR6oySVMpZkcqw2Om9/WBZOk7ysvYTuVabh1Qk2XAYqFQ9Cc8vhn8KTwRJvbNNrSlL2kvShXS2CLY7Yw2lX9FEZ84Ei1p2V7IJi29bERO35RTMDM05uAWLGR/fqnPoExALMDGoe3UBfQYiBgPbb2oMfQIiAiNA3asR9BkIAWbK5rcSHzO@gMTnmOYzYHzq5mN3vAl4HrmjCJeIT/yvLQRQGME8v6Z01sKZwBH219m2X6y7iW653WqX/YKD635fT8bujmHZ2LDC3dvcf/RG8dgsydt6@pHRc13Lkwlt2f8bvpsPGOWhrKri9Gzwb/S9oM9rB@5pL38B "Java (JDK) – Try It Online"

## Explanation

In an array of consecutive numbers, from 1 to n, when the array is riffled, then each value is move its position times 2, modulo the length (if the length is odd) or the length - 1 (if the length is even).

So I'm basically searching for the value 2 using this method.

## Credits

* -8 bytes thanks to [Kevin Cruijssen](https://codegolf.stackexchange.com/users/52210/kevin-cruijssen).