ABC424-D 2x2 Erasing 2

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");
            WillReturn.Add("5 5");
            WillReturn.Add("####.");
            WillReturn.Add("##.##");
            WillReturn.Add("#####");
            WillReturn.Add(".####");
            WillReturn.Add("##.#.");
            WillReturn.Add("2 2");
            WillReturn.Add("..");
            WillReturn.Add("..");
            //3
            //0
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static long[] GetSplitArr(string pStr)
    {
        return (pStr == "" ? new string[0] : pStr.Split(' ')).Select(pX => long.Parse(pX)).ToArray();
    }

    static char[,] mBanArr;
    static long UB_X;
    static long UB_Y;

    static void Main()
    {
        List<string> InputList = GetInputList();
        int CurrInd = 1;

        long[] wkArr = { };
        Action<string> SplitAct = (pStr) => wkArr = GetSplitArr(pStr);

        var sb = new System.Text.StringBuilder();
        while (true) {
            if (CurrInd > InputList.Count - 1) break;
            SplitAct(InputList[CurrInd]);
            long H = wkArr[0];
            long W = wkArr[1];

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

            long Answer = Solve();
            sb.Append(Answer);
            sb.AppendLine();

            CurrInd += (int)H + 1;
        }
        Console.Write(sb.ToString());
    }

    static long Solve()
    {
        UB_X = mBanArr.GetUpperBound(0);
        UB_Y = mBanArr.GetUpperBound(1);

        var Ins_PQueue_Arr = new PQueue_Arr();
        PQueue_Arr.PQueueJyoutaiDef WillEnqueue;
        WillEnqueue.CurrX = 0;
        WillEnqueue.CurrY = 0;
        WillEnqueue.BanArr = mBanArr;
        WillEnqueue.Val = 0;
        Ins_PQueue_Arr.Enqueue(WillEnqueue);

        long Answer = long.MaxValue;
        while (Ins_PQueue_Arr.Count() > 0) {
            PQueue_Arr.PQueueJyoutaiDef Dequeued = Ins_PQueue_Arr.Dequeue();

            if (Dequeued.CurrX > UB_X) {
                Dequeued.CurrX = 0;
                Dequeued.CurrY++;
            }

            // クリア判定
            if (Dequeued.CurrY == UB_Y) {
                Answer = Math.Min(Answer, Dequeued.Val);
                continue;
            }
            if (Answer <= Dequeued.Val) continue;

            long CurrX = Dequeued.CurrX;
            long CurrY = Dequeued.CurrY;

            // 2*2が黒かを判定
            if (Is_2_2_Black(CurrX, CurrY, Dequeued.BanArr)) {
                // 左下を白にする
                WillEnqueue.CurrX = Dequeued.CurrX + 1;
                WillEnqueue.CurrY = Dequeued.CurrY;
                WillEnqueue.BanArr = (char[,])Dequeued.BanArr.Clone();
                WillEnqueue.BanArr[CurrX, CurrY + 1] = '.';
                WillEnqueue.Val = Dequeued.Val + 1;
                Ins_PQueue_Arr.Enqueue(WillEnqueue);

                // 右下を白にする
                WillEnqueue.CurrX = Dequeued.CurrX + 1 + 1;
                WillEnqueue.CurrY = Dequeued.CurrY;
                WillEnqueue.BanArr = (char[,])Dequeued.BanArr.Clone();
                WillEnqueue.BanArr[CurrX + 1, CurrY + 1] = '.';
                WillEnqueue.Val = Dequeued.Val + 1;
                Ins_PQueue_Arr.Enqueue(WillEnqueue);
            }
            else {
                // カレントの移動
                WillEnqueue.CurrX = Dequeued.CurrX + 1;
                WillEnqueue.CurrY = Dequeued.CurrY;
                WillEnqueue.BanArr = Dequeued.BanArr;
                WillEnqueue.Val = Dequeued.Val;
                Ins_PQueue_Arr.Enqueue(WillEnqueue);
            }
        }
        return Answer;
    }

    // 2*2が黒かを判定
    static bool Is_2_2_Black(long pBaseX, long pBaseY, char[,] pBanArr)
    {
        if (pBaseX + 1 > UB_X) return false;
        if (pBaseY + 1 > UB_Y) return false;

        if (pBanArr[pBaseX, pBaseY] == '.') return false;
        if (pBanArr[pBaseX, pBaseY + 1] == '.') return false;
        if (pBanArr[pBaseX + 1, pBaseY] == '.') return false;
        if (pBanArr[pBaseX + 1, pBaseY + 1] == '.') return false;
        return true;
    }

    ////////////////////////////////////////////////////////////////
    // IEnumerable<string>をcharの2次元配列に設定
    ////////////////////////////////////////////////////////////////
    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;
    }
}

#region PQueue_Arr
// 内部で配列使用の優先度付きキュー (根のValが最小)
internal class PQueue_Arr
{
    internal struct PQueueJyoutaiDef
    {
        internal long CurrX;
        internal long CurrY;
        internal char[,] BanArr;
        internal long Val;
    }

    private PQueueJyoutaiDef[] mHeapArr;
    private long mHeapArrCnt = 0;

    // コンストラクタ
    internal PQueue_Arr()
    {
        mHeapArr = new PQueueJyoutaiDef[65535];
    }

    internal bool IsEmpty()
    {
        return mHeapArrCnt == 0;
    }

    internal long Count()
    {
        return mHeapArrCnt;
    }

    internal long Peek()
    {
        return mHeapArr[1].Val;
    }

    // エンキュー処理
    internal void Enqueue(PQueueJyoutaiDef pAddJyoutai)
    {
        long CurrNode = 1 + mHeapArrCnt;
        if (mHeapArr.GetUpperBound(0) < CurrNode) {
            ExtendArr();
        }

        mHeapArr[CurrNode] = pAddJyoutai;
        mHeapArrCnt++;

        while (1 < CurrNode && mHeapArr[CurrNode / 2].Val > mHeapArr[CurrNode].Val) {
            PQueueJyoutaiDef Swap = mHeapArr[CurrNode];
            mHeapArr[CurrNode] = mHeapArr[CurrNode / 2];
            mHeapArr[CurrNode / 2] = Swap;

            CurrNode /= 2;
        }
    }

    // 配列のExtend
    private void ExtendArr()
    {
        PQueueJyoutaiDef[] NewHeapArr = new PQueueJyoutaiDef[mHeapArrCnt * 2];
        mHeapArr.CopyTo(NewHeapArr, 0);
        mHeapArr = NewHeapArr;
    }

    // デキュー処理
    internal PQueueJyoutaiDef Dequeue()
    {
        PQueueJyoutaiDef TopNode = mHeapArr[1];
        long LastNode = mHeapArrCnt;
        mHeapArr[1] = mHeapArr[LastNode];
        mHeapArrCnt--;

        MinHeapify(1);
        return TopNode;
    }

    // 根ノードを指定し、根から葉へヒープ構築
    private void MinHeapify(long pRootNode)
    {
        if (mHeapArrCnt <= 1) {
            return;
        }

        long Left = pRootNode * 2;
        long Right = pRootNode * 2 + 1;

        // 左の子、自分、右の子で値が最小のノードを選ぶ
        long Smallest = mHeapArr[pRootNode].Val;
        long SmallestNode = pRootNode;

        if (Left <= mHeapArrCnt && mHeapArr[Left].Val < Smallest) {
            Smallest = mHeapArr[Left].Val;
            SmallestNode = Left;
        }
        if (Right <= mHeapArrCnt && mHeapArr[Right].Val < Smallest) {
            Smallest = mHeapArr[Right].Val;
            SmallestNode = Right;
        }

        // 子ノードのほうが小さい場合
        if (SmallestNode != pRootNode) {
            PQueueJyoutaiDef Swap = mHeapArr[SmallestNode];
            mHeapArr[SmallestNode] = mHeapArr[pRootNode];
            mHeapArr[pRootNode] = Swap;

            // 再帰的に呼び出し
            MinHeapify(SmallestNode);
        }
    }
}
#endregion

解説

オセロセットで考察し、下記で解いてます。

{CurrX,CurrY,盤面の二次元配列,コスト}を状態に持つ。
座標をZ順で見ていき、2*2の黒マスがあったら、左下と右下の変更を両方試す。
コストが小さい状態優先で、最良優先探索。