ABC178-D Redistribution

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("7");
            //3
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("2");
            //0
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("1729");
            //294867501
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

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

        int S = int.Parse(InputList[0]);

        const int Hou = 1000000000 + 7;

        //場合の数[和]なDP表
        int UB = S;
        int[] DPArr = new int[UB + 1];
        DPArr[0] = 1;
        for (int I = 0; I <= UB; I++) {
            if (DPArr[I] == 0) continue;
            for (int J = 3; J <= S; J++) {
                int NewInd = I + J;
                if (UB < NewInd) break;
                DPArr[NewInd] += DPArr[I];
                DPArr[NewInd] %= Hou;
            }
        }
        Console.WriteLine(DPArr[UB]);
    }
}

解説

動的計画法で解いてます。