利用C#迭代器的一个杨辉三角示例

internal class Program
    {
        /// <summary>
        ///     打印杨辉三角
        /// </summary>
        /// <param name="count"></param>
        /// <returns></returns>
        private static IEnumerable<List<int>> YanghuiSanjiao(int count)
        {
            var previewList = new List<int>();
            List<int> currentList=new List<int>();

            var n = 1;

            while (n <= count)
                if (n == 1 || n == 2)
                {
                    n = n + 1;
                    currentList.Add(1);
                    previewList = currentList;
                    yield return currentList;
                }
                else
                {
                    currentList = new List<int> {1};
                    foreach (var item in Enumerable.Range(1, n - 2))
                        currentList.Add(previewList[item - 1] + previewList[item]);
                    currentList.Add(1);
                    previewList = currentList;
                    n = n + 1;
                    yield return currentList;
                }
        }


        private static void Main(string[] args)
        {
            foreach (var item in YanghuiSanjiao(20))
            {
                item.ForEach(c =>
                {
                    Console.Write(c+" ");
                });
                Console.WriteLine();
            }

            Console.WriteLine("Stop printing");
        }
    }