.NET面试常考算法

通过这几天面试经验来看，发先如下算法考的概率较大。
所以整理如下，供大家参考！

1.求质数
   质数也成为素数，质数就是这个数除了1和他本身两个因数以外，没有其他因数的数，叫做质数，和他相反的是合数，
   就是除了1和他本身两个因数以外，还友其他因数的数叫做合数。

 namespace ConsoleApp
 {
      class Program
      {
         static void Main(string[] args)
         {
             long i;
             while (true)
             {
                 Console.Write("请输入要计算的质数（0退出）：");
                 i = long.Parse(Console.ReadLine());
                 if (i == 0) break;
                 DateTime t1 = DateTime.Now;
                 switch (i)
                 {
                     case 1: Console.WriteLine("1 不是质数！"); break;
                     case 2: Console.WriteLine("2 是质数！"); break;
                     default: cal(i); break;
                 }
                 DateTime t2 = DateTime.Now;
                 Console.WriteLine("时间为：{0} 毫秒
", (t2 - t1).Ticks / 10000f);
             }
         }
 
      //以下为函数部分    
      static void cal(long x)
      {
           long sum = 1;
           byte row = 1;
           Console.Write("
");
           for (long a = 3; a < x + 1; a++)
           {
              bool flag = true;
               for (long b = 2; b < (a / 2) + 1; b++)
               {
                   if (a % b != 0) continue;
                   flag = false;
                   break;
               }
                if (flag)
                {
                   if (row == 10) { Console.WriteLine(); row = 0; }
                   if (sum == 1) Console.Write("{0,7}", 2);
                   Console.Write("{0,7}", a);
                   sum++; row++;
                }
            }
            Console.WriteLine("

{0} 以内共有 {1} 个质数
", x, sum);
       }
     }
 }

2.有一列数1，1，2，3，5，........求第30个数.

  public static int Foo(int i)
    {
       if (i <= 0)
            return 0;
       else if (i > 0 && i <= 2)
            return 1;
       else
            return  Foo(i - 1) + Foo(i - 2);
    }
 

 3.冒泡排序

 //冒泡排序类
  public class sorter
  {
        public void Sort(int[] list)
        {
            int i, j, temp;
            bool done = false;
            j = 1;
            while ((j < list.Length) && (!done))
            {
                done = true;
                for (i = 0; i < list.Length - j; i++)
                {
                    if (list[i] > list[i + 1])
                    {
                        done = false;
                        temp = list[i];
                        list[i] = list[i + 1];
                        list[i + 1] = temp;
                    }
                }
                j++;
            }
        }
    }

//调用代码
 class Program
 {
        static void Main(string[] args)
        {
            int[] arrary = new int[] { 1, 5, 15, 19, 34, 55, 54, 2, 97, 13, 34, 100, 79, 22 };
            sorter sh = new sorter();
            sh.Sort(arrary);
            for (int i = 0; i < arrary.Length; i++)
            {
                Console.Write(arrary[i]);
                Console.Write(",");
            }

            Console.ReadKey();
        }
    }

 4.请编写一个函数，能够计算10以内数的阶乘，尽量采用递归算法。（10!=3628800）。

public int jiecheng(int n)
{
       if (n == 1)
          return 1;
       else if (n == 2)
           return 2;
        else
           return n * jiecheng(n - 1);
}

5 请编程实现此方法。将输入的整型数组，合并转换为逗号分隔的字符串。

   例如输入参数为整型数组{9，7，2}，那么输出结果为字符串"9,7,2"。 

private static string Combine(int[] data)
  {
      string str = "";
      foreach (int s in data)
      {
           str += s.ToString() + ",";
      }
      return str;
  }

 6.产生一个int数组，长度为100，并向其中随机插入1-100，并且不能重复。

//产生一个int数组，长度为100，并向其中随机插入1-100，并且不能重复。
            int[] arr = new int[100];
            ArrayList myList = new ArrayList();
            Random rad = new Random();
            while (myList.Count < 100)
            {
                int num = rad.Next(1, 101);
                if (!myList.Contains(num))
                {
                    myList.Add(num);
                }
            }
            for (int i = 0; i < 100; i++)
            {
                arr[i] = (int)myList[i];
            }
            for (int i = 0; i < arr.Length; i++)
            {
                Console.Write(arr[i] + ",");
            }
            Console.ReadKey();

 7.请将字符串"I am a student"按单词逆序输出 如"student a am I"

string S = "I am a student";
char[] C = new char[] { ' '};
string[] n =S.Split(C);
int length = S.Length;
for (int i =length-1 ; i >=0; i--)
{
        Console.Write(n[i]);
        if (i != 0)
        {
            Console.Write(" ");
        }
}

 8.C# 取两个数组的相同元素

摘要: 以往我们都是肯定绞尽脑汁，肯定什么循环，元素大小，什么因素都考虑进去。但是现在采用Linq可以很好的解决这个问题。找出两个或多个数组的相同项。代码如下：

usingSystem;
 usingSystem.Collections.Generic;
 usingSystem.Linq;
 usingSystem.Text;
 namespaceTest4_03
 {
    classProgram
     {
        staticvoidMain(string[] args)
         {
            string[] names = {"Adams","Arthur","Buchanan","Tsbuchis","ShCian","FuchsiaLinda","DecheChen","Lotheer","FindLanciCade",
            "SorchLand","JiangZheng","MisiiLoda","Gtod","Dfac","Lama","BakCades","Losangle","ZheWQ","GehengDahaLothi","ToryLandey",
            "DakaLothy","BthLanda","MenNorth","Fith","FoxMain","DontM","Saobba","Del","Sala","Ghero","BhthLaPhda"};
            IEnumerable<string> skip = names.Skip(10);
            IEnumerable<string> take = names.Take(11);
            //取出两个序列中交集部分，按理论应该输出JiangZheng
            IEnumerable<string> intersect = skip.Intersect(take);
            foreach(varsinintersect)
             {
                Console.WriteLine(s);
             }
            Console.ReadKey();
         }
     }
 }