ARC110-A Redundant Redundancy

問題へのリンク

C#のソース

using System;
using System.Collections.Generic;

class Program
{
    static string InputPattern = "InputX";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("3");
            //7
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("10");
            //39916801
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        int N = int.Parse(InputList[0]);

        var NumList = new List<int>();

        for (int I = 2; I <= N; I++) {
            NumList.Add(I);
        }

        long CurrLCM = NumList[0];
        for (int I = 1; I <= NumList.Count - 1; I++) {
            long CurrGCD = DeriveGCD(CurrLCM, NumList[I]);
            CurrLCM = CurrLCM * NumList[I] / CurrGCD;
        }
        Console.WriteLine(CurrLCM + 1);
    }

    // ユークリッドの互除法で2数の最大公約数を求める
    static long DeriveGCD(long pVal1, long pVal2)
    {
        long WarareruKazu = pVal2;
        long WaruKazu = pVal1;

        while (true) {
            long Amari = WarareruKazu % WaruKazu;
            if (Amari == 0) return WaruKazu;
            WarareruKazu = WaruKazu;
            WaruKazu = Amari;
        }
    }
}

解説

最小公倍数+1が解なので
最小公倍数を求めてます。