Codwars #4 Find the unique number (6kyu)

There is an array with some numbers. All numbers are equal except for one. Try to find it!

Kata.findUniq(new double[]{ 1, 1, 1, 2, 1, 1 }); // => 2

Kata.findUniq(new double[]{ 0, 0, 0.55, 0, 0 }); // => 0.55

It’s guaranteed that array contains more than 3 numbers.

The tests contain some very huge arrays, so think about performance.

import java.util.Arrays;
import java.util.function.Function;
import java.util.stream.Collectors;

public class Kata {
    public static double findUniq(double arr[]) {
      // Do the magic
      return Arrays.stream(arr).boxed()
             .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
             .entrySet().stream().filter(x->x.getValue()==1)
             .mapToDouble(x->x.getKey()).findFirst().getAsDouble();
    }
}

나름 stream 한번 써보겠다고 열심히 머리굴려서 풀었는데 다른사람 풀이보고 허탈. 문제를 제대로 안읽은 잘못이다. 

가장 많은 추천을 받은 풀이

import java.util.Arrays;
 public class Kata {
    public static double findUniq(double[] arr) {
      Arrays.sort(arr);
      return arr[0] == arr[1] ? arr[arr.length-1]:arr[0];
    }
}