面试题：最后一人开始时的位置？

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            //条件
            int number = 50;
            int interval = 3;
            int[] ids = new int[number];
            for (int i = 0; i < number; i++) ids[i] = 1;

            //辅助变量
            int balance = number;
            int j = 0;

            //报数,3倍数退出
            while (balance != 1)
            {
                for (int k = 0; k < number; k++)
                {
                    if (ids[k] == 0)
                        continue;

                    if (++j % interval == 0)
                    {
                        ids[k] = 0;
                        balance--;

                        if (balance == 1) break;
                    }
                }
            }

            //原来位置查询
            for (int i = 0; i < number; i++)
            {
                if (ids[i] == 1)
                {
                    Console.WriteLine("最后1人开始时的位置为：{0}", i + 1); //11
                    break;
                }
            }

            Console.Read();

        }
    }
}

using System;
using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            //条件
            int number = 50;
            int interval = 3;
            List<int> ids = new List<int>();
            for (int i = 0; i < number; i++) ids.Add(i + 1);


            //辅助变量
            int balance = ids.Count;
            int j = balance;

            //报数,3倍数退出
            while (balance != 1)
            {
                for (int k = balance - 1; k >= 0; k--)
                {
                    if ((j - (balance - k - 1)) % interval == 0)
                        ids.RemoveAt(k);
                }

                balance = ids.Count;
                j += balance;
            }

            //原来位置查询
            Console.WriteLine("最后1人开始时的位置为：{0}", ids[0]); //11

            Console.Read();

        }
    }
}