AOJ 0571 JJOOII

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("OJJOOIIOJOI");
            //2
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("IJJIIJJJ");
            //0
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("JOIJOIJOIJOIJOI");
            //1
        }
        else if (InputPattern == "Input4") {
            WillReturn.Add("OOJJJJJJJOOOOIIIII");
            //4
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        string S = InputList[0];

        List<RunLen.RunLenInfo> RunLenList = RunLen.DeriveRunLenInfoList(S);

        var AnswerList = new List<long>();
        AnswerList.Add(0);
        for (int I = 0; I <= RunLenList.Count - 1; I++) {
            int Ind1 = I;
            int Ind2 = I + 1;
            int Ind3 = I + 2;
            if (Ind3 > RunLenList.Count - 1) continue;

            if (RunLenList[Ind1].AppearChar != 'J') continue;
            if (RunLenList[Ind2].AppearChar != 'O') continue;
            if (RunLenList[Ind3].AppearChar != 'I') continue;

            long JLen = RunLenList[Ind1].RunLen;
            long OLen = RunLenList[Ind2].RunLen;
            long ILen = RunLenList[Ind3].RunLen;

            if (JLen >= OLen && OLen <= ILen) {
                AnswerList.Add(OLen);
            }
        }
        Console.WriteLine(AnswerList.Max());
    }
}

#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

ランレングス圧縮し、
JOIが連続していれば、解候補になりえます。