PermCheck

        /// <summary>
        /// Solution
        /// 100/100
        /// </summary>
        /// <param name="A"></param>
        /// <returns></returns>
        public static int solution(int[] A)
        {
            HashSet<int> hs = new HashSet<int>();
            foreach (int num in A)
            {
                if (!hs.Contains(num) && num <= A.Length)
                    hs.Add(num);
                else
                    return 0;
            }
            return 1;
        }