export default (arr) => {
let max = Math.max.apply(Math, arr)
let min = Math.min.apply(Math, arr)
if (min >= 2) {
return 1
}
if ((min === 0 || min === 1) && ((max - min) === arr.length - 1)) {
return max + 1
}
let nextOne = null
let res
for (let item of arr) {
if (nextOne && nextOne > 0 && nextOne !== item) {
res = Math.min(nextOne, res)
}
nextOne = item + 1
}
res = res ? Math.min(nextOne, res) : nextOne
return res
}