【Python】Codility in Python : Lesson 4 - Counting Elements【MissingInteger】

Counting Elements 練習題的第一題題目是【MissingInteger】
Find the minimal positive integer not occurring in a given sequence.

方法一：使用 in set 判斷內容值的簡易方式
```python def solutionByInSet(A): result = 1 s = set(A) while result in s: result += 1 return result ```

完整練習題 source code 請參閱：github