PermMissingElem - Codibility - C#

PermMissingElem.cs

using System;

namespace PermMissingElem
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] A = new int[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18 };
            var S = new Solution();
            Console.WriteLine($"The missing elem is {S.solution(A)}");
        }
    }

    class Solution
    {
        public int solution(int[] A)
        {
            int low = A[0];
            int high = A[0];

            for(int i = 0; i < A.Length; i++)
            {
                if (A[i] < low) low = A[i];
                if (A[i] > high) high = A[i];
            }

            while(low < high)
            {
                if (Array.IndexOf(A, low) == -1) return low;
                low++;
            }

            return low;
        }
    }
}