# [Algorithm] PermMissingElem

## Question

An 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:

```
function solution(A);
```

that, given an 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.

Write an efficient algorithm for the following assumptions:

- 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)].

## Solution (TypeScript)

```
function solution(n: number[]) {
const tmp = {};
for (let i = 0; i < n.length; i += 1) {
if (!tmp[i + 1]) {
tmp[i + 1] = false;
}
tmp[n[i]] = true;
}
for (let key of Object.keys(tmp)) {
if (!tmp[key]) {
return parseInt(key);
}
}
return n.length + 1;
}
```

Author: Codility, Lesson 3

20200104 Charyum.Park