Donuts プロコンチャレンジ2014 B 7th

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("31");
            //3
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("7");
            //1
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("111");
            //8
        }
        else if (InputPattern == "Input4") {
            WillReturn.Add("777777777777777777");
            //271402266318408
        }
        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 void Main()
    {
        List<string> InputList = GetInputList();
        string StrN = InputList[0];

        // 場合の数[7を法とした余り,数字自由フラグ,0以外登場有無]なDP表
        long[, ,] PrevDP = new long[7, 2, 2];
        PrevDP[0, 0, 0] = 1;

        // 重み[Ind]なDict
        var OmomiDict = new Dictionary<long, long>();
        long Omomi = 1;
        for (long I = StrN.Length - 1; 0 <= I; I--) {
            OmomiDict[I] = Omomi;
            Omomi *= 10;
            Omomi %= 7;
        }

        for (long I = 0; I <= StrN.Length - 1; I++) {
            long[, ,] CurrDP = new long[7, 2, 2];

            for (long J = 0; J <= PrevDP.GetUpperBound(0); J++) {
                for (long K = 0; K <= 1; K++) {
                    for (long L = 0; L <= 1; L++) {

                        if (PrevDP[J, K, L] == 0) continue;

                        for (char NewChar = '0'; NewChar <= '7'; NewChar++) {
                            if (K == 0 && StrN[(int)I] < NewChar) break;

                            long NewJ = J + OmomiDict[I] * (NewChar - '0');
                            NewJ %= 7;

                            long NewK = K;
                            if (StrN[(int)I] > NewChar) NewK = 1;

                            if (L == 1 && NewChar == '0') continue;

                            long NewL = L;
                            if (NewChar != '0' && L == 0) {
                                NewL = 1;
                            }

                            CurrDP[NewJ, NewK, NewL] += PrevDP[J, K, L];
                        }
                    }
                }
            }
            PrevDP = CurrDP;
        }

        long Answer = 0;
        Answer += PrevDP[0, 0, 1];
        Answer += PrevDP[0, 1, 1];
        Console.WriteLine(Answer);
    }
}

解説

桁DPで解いてます。
フル桁でない数を認めるために、
「0以外登場有無」を状態に持ってます。