# codility 3-1. PermMissingElem

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문제출처

## 문제

A zero-indexed array A consisting of N different integers is given. The array contains integers in the range [1..(N + 1)], which means that exactly one element is missing.

Your goal is to find that missing element.

Write a function:

def solution(A)
that, given a zero-indexed array A, returns the value of the missing element.

For example, given array A such that:

A[0] = 2
A[1] = 3
A[2] = 1
A[3] = 5
the function should return 4, as it is the missing element.

Assume that:

N is an integer within the range [0..100,000];
the elements of A are all distinct;
each element of array A is an integer within the range [1..(N + 1)].
Complexity:

expected worst-case time complexity is O(N);
expected worst-case space complexity is O(1), beyond input storage (not counting the storage required for input arguments).
Elements of input arrays can be modified.


## 풀이코드

• Detected time complexity: O(N) or O(N * log(N))
def solution(A):
li = [0] * (len(A) + 1)
for i in A:
li[i-1] = 1
return li.index(0) + 1


## 다른사람 코드

• 와! 이렇게 쉬운 방법이 있었다니..
def solution(A):
return sum (range(len(A)+2)) - sum(A)