- first, create a new int array with order (newAr)
- second, setup newAr's number in nums equal 0.
- find the number in newAr, if not equal 0, then pick up and return.

But I think it has better way to solve it....

```
class Solution {
func findDisappearedNumbers(_ nums: [Int]) -> [Int] {
var newAr = [Int]()
if nums.count < 2{return newAr}
for i in 1...nums.count {
newAr.append(i)
}
for i in 0...nums.count-1 {
newAr[nums[i]-1] = 0
}
var returnAr = [Int]()
for i in 0...newAr.count-1{
if newAr[i] != 0 {
returnAr.append(newAr[i])
}
}
return returnAr;
}
}
```