ABC401-D Logical Filling

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("4 2");
            WillReturn.Add("o???");
            //o.??
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("5 2");
            WillReturn.Add("?????");
            //?????
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("7 3");
            WillReturn.Add(".o???o.");
            //.o.o.o.
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

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

        char[] CharArr = InputList[1].ToCharArray();
        long UB = CharArr.GetUpperBound(0);

        if (CharArr.LongCount(pX => pX == 'o') == K) {
            Console.WriteLine(InputList[1].Replace('?', '.'));
            return;
        }

        for (long I = 0; I <= UB; I++) {
            if (0 < I && CharArr[I - 1] == 'o') {
                CharArr[I] = '.';
            }
            if (I < UB && CharArr[I + 1] == 'o') {
                CharArr[I] = '.';
            }
        }

        List<RunLen.RunLenInfo> RunLenList = RunLen.DeriveRunLenInfoList(new string(CharArr));

        long MaxSum = 0;
        foreach (RunLen.RunLenInfo EachRunLenInfo in RunLenList) {
            if (EachRunLenInfo.AppearChar == 'o') {
                MaxSum += EachRunLenInfo.RunLen;
            }
            if (EachRunLenInfo.AppearChar == '?') {
                long CurrLen = EachRunLenInfo.RunLen;
                if (CurrLen % 2 == 0) {
                    MaxSum += CurrLen / 2;
                }
                else {
                    MaxSum += CurrLen / 2 + 1;
                }
            }
        }

        foreach (RunLen.RunLenInfo EachRunLenInfo in RunLenList) {
            if (EachRunLenInfo.AppearChar == 'o') {
                Console.Write('o');
                continue;
            }
            if (EachRunLenInfo.AppearChar == '.') {
                for (int I = 1; I <= EachRunLenInfo.RunLen; I++) {
                    Console.Write('.');
                }
                continue;
            }
            if (EachRunLenInfo.AppearChar == '?') {
                long OtherLen = MaxSum;
                long CurrLen = EachRunLenInfo.RunLen;
                if (CurrLen % 2 == 0) {
                    OtherLen -= CurrLen / 2;
                }
                else {
                    OtherLen -= CurrLen / 2 + 1;
                }

                if (OtherLen >= K) {
                    for (int I = 1; I <= CurrLen; I++) {
                        Console.Write('?');
                    }
                    continue;
                }

                if (CurrLen % 2 == 0) {
                    for (int I = 1; I <= CurrLen; I++) {
                        Console.Write('?');
                    }
                    continue;
                }

                if (CurrLen % 2 == 1) {
                    if (OtherLen + CurrLen / 2 >= K) {
                        // ?の連続長が奇数長だけど、最大の敷き詰めでなくてもいい場合
                        for (int I = 1; I <= CurrLen; I++) {
                            Console.Write('?');
                        }
                        continue;
                    }
                    for (int I = 1; I <= CurrLen; I++) {
                        // ?の連続長が奇数長で、最大の敷き詰めが必要な場合
                        if (I % 2 == 1) {
                            Console.Write('o');
                        }
                        else {
                            Console.Write('.');
                        }
                    }
                }
            }
        }
        Console.WriteLine();
    }
}

#region RunLen
// ランレングス圧縮(文字列)
internal class RunLen
{
    // ランレングス圧縮情報
    internal struct RunLenInfo
    {
        internal char AppearChar;
        internal int RunLen;
    }

    // ランレングス圧縮結果を返す
    internal static List<RunLenInfo> DeriveRunLenInfoList(string pBaseStr)
    {
        var WillReturn = new List<RunLenInfo>();

        int StrUB = pBaseStr.Length - 1;
        char PrevChar = pBaseStr[0];
        int StrLen = 0;
        for (int I = 0; I <= StrUB; I++) {
            if (pBaseStr[I] != PrevChar) {
                RunLenInfo WillAdd;
                WillAdd.AppearChar = PrevChar;
                WillAdd.RunLen = StrLen;
                WillReturn.Add(WillAdd);
                StrLen = 0;
                PrevChar = pBaseStr[I];
            }
            StrLen++;

            if (I == StrUB) {
                RunLenInfo WillAdd;
                WillAdd.AppearChar = pBaseStr[I];
                WillAdd.RunLen = StrLen;
                WillReturn.Add(WillAdd);
            }
        }
        return WillReturn;
    }
}
#endregion

解説

oの数が既にKの場合
?を.にreplaceし、解が確定します。

oの数がK未満の場合
まず、oの左右は.で確定します。
次に、ランレングス圧縮し、oを最大何個作れるかを求めます。
後は、?の連続数の偶奇に警戒して実装します。