Problem3

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Diagnostics;//输出结果：//最大质数为：6857//所话费的时间为：00:00:02.6578500//The prime factors of 13195 are 5, 7, 13 and 29.//What is the largest prime factor of the number 600851475143 ?//寻找最大质因数namespace Problem3{ class Program { static void Main(string[] args) { Stopwatch sw = new Stopwatch(); sw.Start(); long flag = 0; long target = 600851475143; for (long i = (int)Math.Sqrt(target); i > 0; i--) { if (IsPrime(target)) { flag = target; break; } if (target%i==0&&IsPrime(i)) { flag = i; break; } } Console.WriteLine("最大质数为：{0}", flag); sw.Stop(); Console.WriteLine("所话费的时间为：{0}",sw.Elapsed); } public static bool IsPrime(long l) { for (long i = 2; i < l; i++) { if (l % i == 0) { return false; } } return true; } }}