ABC253-E Distance Sequence

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 3 1");
            //6
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("3 3 2");
            //2
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("100 1000 500");
            //657064711
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    const long Hou = 998244353;

    static void Main()
    {
        List<string> InputList = GetInputList();
        long[] wkArr = InputList[0].Split(' ').Select(pX => long.Parse(pX)).ToArray();
        long N = wkArr[0];
        long M = wkArr[1];
        long K = wkArr[2];
        long UB = M;

        // 場合の数[最終値]なDP表
        long[] PrevDP = new long[UB + 1];
        PrevDP[1] = 1;

        for (long I = 2; I <= N; I++) {
            long[] CurrDP = new long[UB + 1];
            long RunSum = 0;
            for (long J = 0; J <= UB; J++) {
                RunSum += PrevDP[J];
                RunSum %= Hou;

                long ImosEnd1 = J - K + 1;
                long ImosSta2 = J + K;

                if (1 <= ImosEnd1 && ImosEnd1 <= UB) {
                    CurrDP[1] += RunSum;
                    CurrDP[1] %= Hou;
                    CurrDP[ImosEnd1] -= RunSum;
                    if (CurrDP[ImosEnd1] < 0) {
                        CurrDP[ImosEnd1] += Hou;
                    }
                }

                if (ImosSta2 <= UB) {
                    CurrDP[ImosSta2] += RunSum;
                    CurrDP[ImosSta2] %= Hou;
                }
            }
            PrevDP = CurrDP;
        }

        long Answer = 0;
        long RunSum2 = 0;
        for (long J = 0; J <= UB; J++) {
            RunSum2 += PrevDP[J];
            RunSum2 %= Hou;
            Answer += RunSum2;
            Answer %= Hou;
        }
        Console.WriteLine(Answer);
    }
}

解説

配るDPで解いてます。
配る先が連続した区間なので、いもす法で配ってます。