ABC307-E Distinct Adjacent

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("3 3");
            //6
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("4 2");
            //2
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("987654 456789");
            //778634319
        }
        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 mN = wkArr[0];
        long mM = wkArr[1];

        // 場合の数[先頭と同じか？]なDP表
        long[] PrevDP = new long[2];
        PrevDP[0] = mM * (mM - 1);
        PrevDP[0] %= Hou;

        for (long I = 3; I <= mN; I++) {
            long[] CurrDP = new long[2];

            for (long J = 0; J <= 1; J++) {
                if (PrevDP[J] == 0) continue;

                if (J == 0) {
                    CurrDP[0] += PrevDP[J] * (mM - 2);
                    CurrDP[0] %= Hou;
                    CurrDP[1] += PrevDP[J];
                    CurrDP[1] %= Hou;
                }
                if (J == 1) {
                    CurrDP[0] += PrevDP[J] * (mM - 1);
                    CurrDP[0] %= Hou;
                }
            }
            PrevDP = CurrDP;
        }
        Console.WriteLine(PrevDP[0]);
    }
}

解説

場合の数[先頭と同じか？]
を更新するDPで解いてます。