AOJ 0569 イルミネーション

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("8 4");
            WillReturn.Add("0 1 0 1 0 1 1 1");
            WillReturn.Add("0 1 1 0 0 1 0 0");
            WillReturn.Add("1 0 1 0 1 1 1 1");
            WillReturn.Add("0 1 1 0 1 0 1 0");
            //64
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("8 5");
            WillReturn.Add("0 1 1 1 0 1 1 1");
            WillReturn.Add("0 1 0 0 1 1 0 0");
            WillReturn.Add("1 0 0 1 1 1 1 1");
            WillReturn.Add("0 1 0 1 1 0 1 0");
            WillReturn.Add("0 1 1 0 1 1 0 0");
            //56
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static Dictionary<int, int> mHexDict = new Dictionary<int, int>();

    static void Main()
    {
        List<string> InputList = GetInputList();
        int[,] OldBanArr = CreateBanArr(InputList.Skip(1));

        int Old_UB_X = OldBanArr.GetUpperBound(0);
        int Old_UB_Y = OldBanArr.GetUpperBound(1);

        int UB_X = Old_UB_X + 2;
        int UB_Y = Old_UB_Y + 2;

        // 外周を0で囲う
        int[,] BanArr = new int[UB_X + 1, UB_Y + 1];
        for (int LoopX = 0; LoopX <= Old_UB_X; LoopX++) {
            for (int LoopY = 0; LoopY <= Old_UB_Y; LoopY++) {
                BanArr[LoopX + 1, LoopY + 1] = OldBanArr[LoopX, LoopY];
            }
        }

        for (int LoopX = 0; LoopX <= UB_X; LoopX++) {
            for (int LoopY = 0; LoopY <= UB_Y; LoopY++) {
                int HexHash = GetHexHash(LoopX, LoopY);
                mHexDict[HexHash] = BanArr[LoopX, LoopY];
            }
        }

        HashSet<int> VisitedSet = ExecBFS();

        // 黒マスごとに6辺の中で、外周の白マスと隣接した辺を数える
        int Answer = 0;
        foreach (var EachPair in mHexDict) {
            if (EachPair.Value != 1) continue;
            int CurrHexX = EachPair.Key / Geta;
            int CurrHexY = EachPair.Key % Geta;

            Action<int, int> CntAct = (pRinsetuX, pRinsetuY) =>
            {
                int RinsetuHash = GetHash(pRinsetuX, pRinsetuY);
                if (VisitedSet.Contains(RinsetuHash)) {
                    Answer++;
                }
            };

            CntAct(CurrHexX - 2, CurrHexY);
            CntAct(CurrHexX + 2, CurrHexY);

            CntAct(CurrHexX - 1, CurrHexY - 1);
            CntAct(CurrHexX + 1, CurrHexY - 1);

            CntAct(CurrHexX - 1, CurrHexY + 1);
            CntAct(CurrHexX + 1, CurrHexY + 1);
        }
        Console.WriteLine(Answer);
    }

    // 外周と隣接した白マスをBFSで列挙
    static HashSet<int> ExecBFS()
    {
        var Que = new Queue<JyoutaiDef>();
        JyoutaiDef WillEnqueue;
        int StaHash = GetHexHash(0, 0);
        WillEnqueue.CurrHexHash = StaHash;
        Que.Enqueue(WillEnqueue);

        var VisitedSet = new HashSet<int>();
        VisitedSet.Add(StaHash);

        while (Que.Count > 0) {
            JyoutaiDef Dequeued = Que.Dequeue();

            int CurrHexX = Dequeued.CurrHexHash / Geta;
            int CurrHexY = Dequeued.CurrHexHash % Geta;

            Action<int, int> EneueueAct = (pNewHexX, pNewHexY) =>
            {
                int NewHash = GetHash(pNewHexX, pNewHexY);
                if (mHexDict.ContainsKey(NewHash) == false) {
                    return;
                }
                if (mHexDict[NewHash] == 1) {
                    return;
                }

                if (VisitedSet.Add(NewHash)) {
                    WillEnqueue.CurrHexHash = NewHash;
                    Que.Enqueue(WillEnqueue);
                }
            };

            EneueueAct(CurrHexX - 2, CurrHexY);
            EneueueAct(CurrHexX + 2, CurrHexY);

            EneueueAct(CurrHexX - 1, CurrHexY - 1);
            EneueueAct(CurrHexX + 1, CurrHexY - 1);

            EneueueAct(CurrHexX - 1, CurrHexY + 1);
            EneueueAct(CurrHexX + 1, CurrHexY + 1);
        }
        return VisitedSet;
    }

    struct JyoutaiDef
    {
        internal int CurrHexHash;
    }

    // 2次元座標のXとYを引数として、6角座標のXとYからなるハッシュ値を返す
    static int GetHexHash(int pX, int pY)
    {
        int HexX;
        int HexY = pY;

        if (pY % 2 == 0) {
            HexX = 2 * pX;
        }
        else {
            HexX = 2 * pX + 1;
        }

        return GetHash(HexX, HexY);
    }

    // 6各座標のXとYを引数として、ハッシュ値を返す
    const int Geta = 1000;
    static int GetHash(int pHexX, int pHexY)
    {
        return pHexX * Geta + pHexY;
    }

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

        int[] IntArr = { };
        Action<string> SplitAct = pStr =>
            IntArr = pStr.Split(' ').Select(pX => int.Parse(pX)).ToArray();

        SplitAct(StrList[0]);

        int UB_X = IntArr.GetUpperBound(0);
        int UB_Y = StrList.Count - 1;

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

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

解説

白黒白黒白黒黒黒
白黒黒白白黒白白
黒白黒白黒黒黒黒
白黒黒白黒白黒白

で考えると、最初に外周を白で囲います。
白白白白白白白白白白
白白黒白黒白黒黒黒白
白白黒黒白白黒白白白
白黒白黒白黒黒黒黒白
白白黒黒白黒白黒白白
白白白白白白白白白白

BFSで左上の白と隣接した座標を列挙します。
黒マスごとにこれを隣接した白マスの数を集計します。

これらをHex座標で行えば解けます。