Peaks【★★★】

        /// <summary>
        /// Solution
        /// 100/100
        /// </summary>
        /// <param name="A"></param>
        /// <returns></returns>
        public int solution(int[] A)
        {
            HashSet<int> peakIds = new HashSet<int>();

            for (int i = 1; i < A.Length - 1; i++)
                if (A[i] > A[i - 1] && A[i] > A[i + 1])
                    peakIds.Add(i);

            for (int size = 2; size <= A.Length; size++)
            {
                if (A.Length % size == 0)
                {
                    int groups = A.Length / size;
                    int flag = 0;
                    foreach (int peakId in peakIds)
                    {
                        if (peakId / size > flag)
                            break;
                        if (peakId / size == flag)
                            flag++;
                    }
                    if (flag == groups) return groups;
                }
            }
            return 0;
        }