find-the-missing-integer in array c#

This is a demo task.

Write a function:

class Solution { public int solution(int[] A); }

that, given an array A of N integers, returns the smallest positive integer (greater than 0) that does not occur in A.

For example, given A = [1, 3, 6, 4, 1, 2], the function should return 5.

Given A = [1, 2, 3], the function should return 4.

Given A = [−1, −3], the function should return 1.

Write an efficient algorithm for the following assumptions:

• N is an integer within the range [1..100,000];
• each element of array A is an integer within the range [−1,000,000..1,000,000].

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 using System;

using System.Collections.Generic;

// you can also use other imports, for example:

// using System.Collections.Generic;

// you can write to stdout for debugging purposes, e.g.

// Console.WriteLine("this is a debug message");

class Solution {

    public int solution(int[] A) {

      

      

       HashSet<int> found = new HashSet<int>();

            for (int i = 0; i < A.Length; i++)

            {

                if (A[i] > 0)

                {

                    found.Add(A[i]);

                }

            }

            int result = 1;

            while (found.Contains(result))

            {

                result++;

            }

            return result;

        }

}