Which is missing? (2) X90391

Statement

We handle lists that contain $n-1$ integers, all between $0$ and $n-1$ (both included), and all different. Therefore, exactly one of these $n$ numbers is missing. Which one?

Write a function $missing(lst)$ that receives such a list and returns the missing number.

Precondition: we are ensured that the list $lst$ received by the function will always fulfill the condition that it contains nonnegative integers less than $n$ , all different, where $n$ is one more than the length of $lst$ (hence, $n > 0$ is also guaranteed as the smallest list has length zero).

Sample session

>>> missing([2, 1, 0, 4])
3
>>> missing([1])
0
>>> missing([0, 1])
2
>>> missing([4, 3, 5, 6, 0, 1, 8, 9, 7])
2
>>> missing([])
0

Information

Author: Jordi Petit (adapted by José Luis Balcázar)
Language: English
Official solutions: Python
User solutions: Python