C#

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// --------------------------------------------------------------------------------------------------------------------
// <copyright file="Program.cs" company="Chimomo's Company">
// Respect the work.
// </copyright>
// <summary>
// The program.
// </summary>
// --------------------------------------------------------------------------------------------------------------------
namespace CSharpLearning
{
using System;
/// <summary>
/// The program.
/// </summary>
public static class Program
{
/// <summary>
/// The main.
/// </summary>
/// <param name="args">
/// The args.
/// </param>
public static void Main(string[] args)
{
string fac100 = Factorial(100).ToString("F0");
Console.WriteLine("The factorial of 100 is : {0}", fac100);
for (int i = 0; i <= fac100.Length - 4; i++)
{
string substr = fac100.Substring(i, 4);
if (CheckPrime(Convert.ToInt32(substr)))
{
Console.WriteLine("The expected result found and it is : " + substr);
return;
}
}
Console.WriteLine("No result as expected!!");
}
/// <summary>
/// The factorial.
/// </summary>
/// <param name="n">
/// The n.
/// </param>
/// <returns>
/// The <see cref="double"/>.
/// </returns>
public static double Factorial(int n)
{
double result = 1;
for (int i = 1; i <= n; i++)
{
result *= i;
}
return result;
}
/// <summary>
/// The check prime.
/// </summary>
/// <param name="n">
/// The n.
/// </param>
/// <returns>
/// The <see cref="bool"/>.
/// </returns>
public static bool CheckPrime(int n)
{
if (n == 1 || n == 2)
{
return true;
}
int squareRoot = Convert.ToInt32(Math.Sqrt(n));
for (int i = squareRoot; i > 1; i--)
{
if (n % i == 0)
{
return false;
}
}
return true;
}
}
}
// Output:
/*
The factorial of 100 is : 93326215443944100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
The expected result found and it is : 2621

*/
转自：http://blog.csdn.net/troubleshooter/article/details/5506027

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