# Codility - PermMissingElem

Oct 30, 2015 · 1 minute read · Commentscodilitytil

https://codility.com/programmers/task/perm_missing_elem

### My solution

```
def solution(a)
return 1 if a.empty?
# edge case, N + 1 is missing
# but unlike the case below, we can immediately compute and return this
if a.length == 1
return 2 if a[0] == 1
return 1 if a[0] == 2
end
sorted = a.sort
sorted.each_index do |index|
return index + 1 if(sorted[index] != index + 1)
end
# edge case, N + 1 is missing
return a.length + 1
end
```

### Learning points

- Edge cases are always tricky! Always get into the habit of asking: what can go wrong? Good questions to ask are: what about empty inputs, beginning/ending elements are missing.
- I have a feeling that for the other languages, you need to implement your own sorting algorithm (like bubble sort).