[codillity] kotlin - lesson3. PermMissingElem

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:

class Solution { public int solution(int[] 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)].

 

private fun solution(A: IntArray): Int {
    // O(N) or O(N*log(N))
    if(A.isEmpty()){
        return 1
    }
    A.sort()
    if(A.first() != 1){
        return 1
    }
    var temp = 1
    A.forEach {
        if(temp == it){
            temp +=1
        }else{
            return temp
        }
    }
    if(temp == 1) {
        temp = A.size
    }
    return temp
}