AOJ 0598 JOI 紋章

問題へのリンク(AOJ)
問題へのリンク(AtCoder)

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 5");
            WillReturn.Add("JOIJO");
            WillReturn.Add("IJOOO");
            WillReturn.Add("IIJIJ");
            WillReturn.Add("JO");
            WillReturn.Add("IJ");
            //3
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("2 6");
            WillReturn.Add("JOJOJO");
            WillReturn.Add("OJOJOJ");
            WillReturn.Add("OJ");
            WillReturn.Add("JO");
            //2
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("2 2");
            WillReturn.Add("JI");
            WillReturn.Add("IJ");
            WillReturn.Add("JJ");
            WillReturn.Add("JJ");
            //0
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static char[,] mBanArr;
    static char[,] mGoalArr;

    static int UB_X;
    static int UB_Y;

    static void Main()
    {
        List<string> InputList = GetInputList();
        int[] wkArr = InputList[0].Split(' ').Select(pX => int.Parse(pX)).ToArray();
        int H = wkArr[0];
        int W = wkArr[1];

        mBanArr = CreateBanArr(InputList.Skip(1).Take(H));
        mGoalArr = CreateBanArr(InputList.Skip(1 + H));

        UB_X = mBanArr.GetUpperBound(0);
        UB_Y = mBanArr.GetUpperBound(1);

        // 初期状態での紋章の座標のハッシュ値の集合
        var DefalstMonsyouSet = new HashSet<long>();
        for (int LoopX = 0; LoopX <= UB_X; LoopX++) {
            for (int LoopY = 0; LoopY <= UB_Y; LoopY++) {
                if (IsMonsyou(LoopX, LoopY)) {
                    DefalstMonsyouSet.Add(GetHash(LoopX, LoopY));
                }
            }
        }

        int DefaultCnt = DefalstMonsyouSet.Count;

        var AnswerList = new List<int>();
        AnswerList.Add(DefaultCnt);

        var CharList = new List<char>() { 'J', 'O', 'I' };
        for (int LoopX = 0; LoopX <= UB_X; LoopX++) {
            for (int LoopY = 0; LoopY <= UB_Y; LoopY++) {
                char BeforeChar = mBanArr[LoopX, LoopY];

                foreach (char EachAfterChar in CharList) {
                    if (EachAfterChar == BeforeChar) continue;
                    mBanArr[LoopX, LoopY] = EachAfterChar;

                    int AnswerCnt = DefaultCnt;

                    Action<int, int> CntAct = (pBaseX, pBaseY) =>
                    {
                        long Hash = GetHash(pBaseX, pBaseY);
                        if (DefalstMonsyouSet.Contains(Hash)) AnswerCnt--;

                        if (IsMonsyou(pBaseX, pBaseY)) {
                            AnswerCnt++;
                        }
                    };
                    CntAct(LoopX, LoopY);
                    CntAct(LoopX - 1, LoopY);
                    CntAct(LoopX, LoopY - 1);
                    CntAct(LoopX - 1, LoopY - 1);
                    AnswerList.Add(AnswerCnt);

                    mBanArr[LoopX, LoopY] = BeforeChar;
                }
            }
        }
        Console.WriteLine(AnswerList.Max());
    }

    static long GetHash(int pX, int pY)
    {
        long Hash = pX;
        Hash *= 100000000;
        Hash += pY;
        return Hash;
    }

    // JOI紋章の左上候補の座標を引数とし、JOI紋章かを返す
    static bool IsMonsyou(int pBaseX, int pBaseY)
    {
        if (pBaseX < 0 || UB_X < pBaseX) return false;
        if (pBaseY < 0 || UB_Y < pBaseY) return false;

        for (int LoopX = pBaseX; LoopX <= pBaseX + 1; LoopX++) {
            if (UB_X < LoopX) return false;
            for (int LoopY = pBaseY; LoopY <= pBaseY + 1; LoopY++) {
                if (UB_Y < LoopY) return false;

                int XVect = LoopX - pBaseX;
                int YVect = LoopY - pBaseY;
                if (mGoalArr[XVect, YVect] != mBanArr[LoopX, LoopY]) {
                    return false;
                }
            }
        }
        return true;
    }

    ////////////////////////////////////////////////////////////////
    // IEnumerable<string>をcharの2次元配列に設定する
    ////////////////////////////////////////////////////////////////
    static char[,] CreateBanArr(IEnumerable<string> pStrEnum)
    {
        var StrList = pStrEnum.ToList();
        if (StrList.Count == 0) {
            return new char[0, 0];
        }
        int UB_X = StrList[0].Length - 1;
        int UB_Y = StrList.Count - 1;

        char[,] WillReturn = new char[UB_X + 1, UB_Y + 1];

        for (int Y = 0; Y <= UB_Y; Y++) {
            for (int X = 0; X <= UB_X; X++) {
                WillReturn[X, Y] = StrList[Y][X];
            }
        }
        return WillReturn;
    }
}

解説

□□□□
□□□□
□□□□
□□□□

2次元グリッドで考えると
マス目を変更したら、変更したマス目に下記の変位ベクトルを足した座標を
2*2の紋章の左上として、そこが紋章になったかを再度調べれば良いです。
(-1,-1)
(-1, 0)
( 0,-1)
( 0, 0)