A26 Prime Check

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("4");
            WillReturn.Add("17");
            WillReturn.Add("31");
            WillReturn.Add("35");
            WillReturn.Add("49");
            //Yes
            //Yes
            //No
            //No
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        int[] XArr = InputList.Skip(1).Select(pX => int.Parse(pX)).ToArray();

        int MaxX = XArr.Max();

        Eratosthenes(MaxX);

        foreach (int EachX in XArr) {
            if (Array.BinarySearch(mSosuuArr, EachX) >= 0) {
                Console.WriteLine("Yes");
            }
            else {
                Console.WriteLine("No");
            }
        }
    }

    static long[] mSosuuArr;

    // エラトステネスの篩
    static void Eratosthenes(long pJyougen)
    {
        bool[] IsSosuuArr = new bool[pJyougen + 1];
        for (int I = 2; I <= IsSosuuArr.GetUpperBound(0); I++) {
            IsSosuuArr[I] = true;
        }
        for (int I = 2; I * I <= IsSosuuArr.GetUpperBound(0); I++) {
            if (IsSosuuArr[I]) {
                for (int J = I * 2; J <= IsSosuuArr.GetUpperBound(0); J += I) {
                    IsSosuuArr[J] = false;
                }
            }
        }

        var SosuuList = new List<long>();
        for (int I = 2; I <= IsSosuuArr.GetUpperBound(0); I++) {
            if (IsSosuuArr[I]) SosuuList.Add(I);
        }

        mSosuuArr = SosuuList.ToArray();
    }
}

解説

エラトステネスの篩を使ってます。