算法面试题

1. C# 1到100,每三个数 ,取第三个数,直到输出最后一个数。

注释：比如1-100，第一次输出的数就是3，6，9，12，15，18.....99，第二次输出的就是9，18，27，36，45，....99，直到最后输出为一个数。

别人的写法：

class Program
    {
        static void Main(string[] args)
        {
            List<int> list = new List<int>();
            InitList(list);
            RemoveIt(ref list);
            for (int i = 0; i < list.Count; i++)
                Console.WriteLine(list[i]);
            Console.ReadLine();
        }
        static void InitList(List<int> list)
        {
            for (int i = 1; i <= 100; i++)
                list.Add(i);
        }
        static void RemoveIt(ref List<int>  list)
        {
            List<int> result = new List<int>();
            for (int i = 1; i <= list.Count; i++)
            {
                if (i % 3 == 0)
                {
                    result.Add(list[i - 1]);
                    if (result.Count > 1) Console.Write(","); 
                    Console.Write(list[i - 1]);
                }
            }
            Console.WriteLine();
            list = result;
            if (list.Count >= 3) RemoveIt(ref list);
        }
    }

自己的写法：

class Program
   {
       static void Main(string[] args)
       {
           Dictionary<int, int> dic = new Dictionary<int, int>();
           for (int i = 1; i < 101; i++)
           {
               dic.Add(i, i);
           }
 
           while (true)
           {
               dic = run(dic);
               if (dic.Count == 1)
               {
                   break;
               }
           }
           Console.ReadKey();
       }
 
       private static Dictionary<int, int> run(Dictionary<int, int> num)
       {
           int count = 0;
           int dicIndex = 1;
           Dictionary<int, int> dic = new Dictionary<int, int>();
           foreach (var item in num)
           {
               count++;
               if (count == 3)
               {
                   count = 0;
                   dic.Add(dicIndex, item.Value);
                   dicIndex++;
               }
           }
 
           //打印验证数据准确性
           foreach (var item in dic)
           {
               Console.WriteLine(item.Key + ":" + item.Value);
           }
           Console.WriteLine("\r\n");
 
           return dic;
       }
   }

2.54张牌洗牌算法：

class Program
{
    static void Main(string[] args)
    {
        int[] numbers = new int[54];
        int length = numbers.Length;
        for (int i = 0; i < length; i++)
        {
            numbers[i] = i + 1;
        }
 
        random(numbers, length);
        foreach (int i in numbers)
        {
            Console.Write(i + " ");
        }
        Console.ReadKey();
    }
 
    private static void random(int[] array, int length)
    {
        int index;
        int value;
        for (int i = length - 1; i > 0; i--)
        {
            index = new Random().Next(0, i + 1);
 
            value = array[i];
            array[i] = array[index];
            array[index] = value;
        }
    }
}

3.数据由小到大排序

一般的算法

int[] nums = new int[] { 56, 2, 65, 36, 21, 3, 5, 4, 6, 54, 88 };
      for (int i = 0; i < nums.Length - 1; i++)
      {
          for (int j = 0; j < nums.Length - 1 - i; j++)
          {
              if (nums[j] > nums[j + 1])
              {
                  int temp = nums[j];
                  nums[j] = nums[j + 1];
                  nums[j + 1] = temp;
              }
          }
      }
      foreach (var n in nums)
      {
          Console.WriteLine(n);
      }
      Console.ReadKey();

用Linq也可以实现

int[] nums = new int[] { 56, 2, 65, 36, 21, 3, 5, 4, 6, 54, 88 };
           var result = from c in nums.ToList()
                        orderby c 
                        select c;
           foreach (var n in result)
           {
               Console.WriteLine(n);
           }
 
           Console.ReadKey();