ABC247-C 1 2 1 3 1 2 1

問題へのリンク

C#のソース

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

class Program
{
    static string InputPattern = "InputX";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("2");
            //1 2 1
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("1");
            //1
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("4");
            //1 2 1 3 1 2 1 4 1 2 1 3 1 2 1
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        int N = int.Parse(InputList[0]);

        var PrevList = new List<int>();
        PrevList.Add(1);
        for (int I = 2; I <= N; I++) {
            var CurrList = new List<int>();
            CurrList.AddRange(PrevList);
            CurrList.Add(I);
            CurrList.AddRange(PrevList);
            PrevList = CurrList;
        }
        Console.WriteLine(IntEnumJoin(" ", PrevList));
    }

    ////////////////////////////////////////////////////////////////
    // セパレータとInt型の列挙を引数として、結合したstringを返す
    ////////////////////////////////////////////////////////////////
    static string IntEnumJoin(string pSeparater, IEnumerable<int> pEnum)
    {
        string[] StrArr = Array.ConvertAll(pEnum.ToArray(), pX => pX.ToString());
        return string.Join(pSeparater, StrArr);
    }
}

解説

ListのAddRangeメソッドを使ってます。