def distinctBy[B, C](xs: List[B], f: B => C, acc: List[C] = Nil): List[B] = xs match {+
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  case Nil => Nil+
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  case (x::xs) => {+
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    val res = f(x)+
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    if (acc.contains(res)) distinctBy(xs, f, acc)  +
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    else x::distinctBy(xs, f, res::acc)+
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  }+
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} +
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+
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+
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+
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