Q.

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

findUniq([ 1, 1, 1, 2, 1, 1 ]) === 2
findUniq([ 0, 0, 0.55, 0, 0 ]) === 0.55
It’s guaranteed that array contains at least 3 numbers.

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

A)

function findUniq(arr) {
  // do magic
  let arrIdx = [...new Set([...arr])]
  return arr.indexOf(arrIdx[0]) === arr.lastIndexOf(arrIdx[0]) ? arrIdx[0] : arrIdx[1]
}

오..내가 생각해도 좀 잘 짠듯