.NET面试常考算法

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。

 1  namespace ConsoleApp
 2  {
 3       class Program
 4       {
 5          static void Main(string[] args)
 6          {
 7              long i;
 8              while (true)
 9              {
10                  Console.Write("请输入要计算的质数（0退出）：");
11                  i = long.Parse(Console.ReadLine());
12                  if (i == 0) break;
13                  DateTime t1 = DateTime.Now;
14                  switch (i)
15                  {
16                      case 1: Console.WriteLine("1 不是质数！"); break;
17                      case 2: Console.WriteLine("2 是质数！"); break;
18                      default: cal(i); break;
19                  }
20                  DateTime t2 = DateTime.Now;
21                  Console.WriteLine("时间为：{0} 毫秒\n", (t2 - t1).Ticks / 10000f);
22              }
23          }
24  
25       //以下为函数部分    
26       static void cal(long x)
27       {
28            long sum = 1;
29            byte row = 1;
30            Console.Write("\n");
31            for (long a = 3; a < x + 1; a++)
32            {
33               bool flag = true;
34                for (long b = 2; b < (a / 2) + 1; b++)
35                {
36                    if (a % b != 0) continue;
37                    flag = false;
38                    break;
39                }
40                 if (flag)
41                 {
42                    if (row == 10) { Console.WriteLine(); row = 0; }
43                    if (sum == 1) Console.Write("{0,7}", 2);
44                    Console.Write("{0,7}", a);
45                    sum++; row++;
46                 }
47             }
48             Console.WriteLine("\n\n{0} 以内共有 {1} 个质数\n", x, sum);
49        }
50      }
51  }

2.有一列数1，1，2，3，5，........求第30个数.

 1   public static int Foo(int i)
 2     {
 3        if (i <= 0)
 4             return 0;
 5        else if (i > 0 && i <= 2)
 6             return 1;
 7        else
 8             return  Foo(i - 1) + Foo(i - 2);
 9     }
10  

 3.冒泡排序

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//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(); } }

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 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）。

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

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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"。 

1 private static string Combine(int[] data)
2   {
3       string str = "";
4       foreach (int s in data)
5       {
6            str += s.ToString() + ",";
7       }
8       return str;
9   }

 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。

 1 //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。
 2             int[] arr = new int[100];
 3             ArrayList myList = new ArrayList();
 4             Random rad = new Random();
 5             while (myList.Count < 100)
 6             {
 7                 int num = rad.Next(1, 101);
 8                 if (!myList.Contains(num))
 9                 {
10                     myList.Add(num);
11                 }
12             }
13             for (int i = 0; i < 100; i++)
14             {
15                 arr[i] = (int)myList[i];
16             }
17             for (int i = 0; i < arr.Length; i++)
18             {
19                 Console.Write(arr[i] + ",");
20             }
21             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();
         }
     }
 }