利用yield关键字输出杨辉三角

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication2
{
    class Program
    {

        static void Main(string[] args)
        {
            foreach (var obj in YHSJ(8))
            {
                PrintRow(obj);
            }
            Console.ReadKey();
        }

        /// <summary>
        /// 取得杨辉三角的迭代器
        /// </summary>
        /// <param name="n"></param>
        /// <returns></returns>
        public static IEnumerable<IEnumerable<int>> YHSJ(int n)
        {
            //第一行
            List<int> row = new List<int> { 1 };
            yield return row;
            //第二行
            row = new List<int> { 1, 1 };
            yield return row;
            //第三行及其之后的
            while (n > 0)
            {
                List<int> newrow = new List<int> { 1, 1 };
                int index = row.Count;
                for (int i = 1; i < index; i++)
                {
                    newrow.Insert(1, row[i - 1] + row[i]);
                }
                yield return newrow;
                row = newrow;
                n--;
            }
        }

        /// <summary>
        /// 打印一行数据
        /// </summary>
        /// <param name="row"></param>
        public static void PrintRow(IEnumerable<int> row)
        {
            foreach (int i in row)
            {
                Console.Write(i + "\t");
            }
            Console.WriteLine();
        }
    }
}