ABC164-D Multiple of 2019

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("1817181712114");
            //3
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("14282668646");
            //2
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("2119");
            //0
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

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

        int UB = 2018;

        // 場合の数[mod 2019]なDP表
        int[] PrevDP = new int[UB + 1];

        long Answer = 0;

        for (int I = 0; I <= S.Length - 1; I++) {
            int[] CurrDP = new int[UB + 1];

            int CurrNum = S[I] - '0';
            CurrDP[CurrNum]++;

            for (int J = 0; J <= UB; J++) {
                if (PrevDP[J] == 0) continue;

                int NewInd = J * 10 + CurrNum;
                NewInd %= 2019;
                CurrDP[NewInd] += PrevDP[J];
            }
            // 解を計上
            Answer += CurrDP[0];

            PrevDP = CurrDP;
        }
        Console.WriteLine(Answer);
    }
}

解説

解を計上していくタイプの動的計画法で解いてます。