Yes it is

Yup, that's the math way to do it.

Hello, thank you for your answer.

I just saw the example tests:

names1 = ["Sheldon", "Leonard", "Penny", "Rajesh", "Howard"]
r1 = 1
res1 = "Sheldon"
names2 = ["Sheldon", "Leonard", "Penny", "Rajesh", "Howard"]
r2 = 6
res2 = "Howard"
names3 = ["Sheldon", "Leonard", "Penny", "Rajesh", "Howard"]
r3 = 10
res3 = "Penny"
Test.assertEquals(whoIsNext(names1, r1), res1)
Test.assertEquals(whoIsNext(names2, r2), res2)
Test.assertEquals(whoIsNext(names3, r3), res3)

Your ruby and java version have r=6 , res=Sheldon indeed, maybe it's a cache thing or something because it has been a while since I've tried to solve it.