func isRotation(_ s1: String, _ s2: String) -> Bool {
return (s1.count == s2.count) && (s1 + s1).contains(s2)
}
var s1 = "abbc"
var s2 = "cabb"
print(isRotation(s1, s2) ? "yes" : "no")
s1 = "abbc"
s2 = "bbac"
print(isRotation(s1, s2) ? "yes" : "no")
/*
run:
yes
no
*/