namespace 面试常见算法

{

    class Program

    {

        static void Main(string[] args)

        {

            int n1 = Test1();

            Console.WriteLine(n1);

            Test2();

            Test3();

            int n2 = Test4();

            Console.WriteLine(n2);

            string s = Test5();

            Console.WriteLine(s);

            Test6();

            Test7();

            Console.ReadKey();

        }

        #region//1-2+3-4+...+m

        static int Test1(int m)

        {

            int sum = ;

            for (int i = ; i <= m; i++)

            {

                if (i %  > )   //奇偶性判断

                {

                    sum += i;

                }

                else

                {

                    sum -= i;

                }

            }

            return sum;

        }

        #endregion

        #region//1，2，3，4四个数字，能够组成多少互不相同无重复数字的三位数

        static void Test2()

        {

            int count = ;

            for (int bw = ; bw <= ; bw++)

            {

                for (int sw = ; sw <= ; sw++)

                {

                    if (sw != bw)

                    {

                        for (int gw = ; gw <= ; gw++)

                        {

                            if (gw != sw && gw != bw)

                            {

                                count++;

                                Console.WriteLine("{0}{1}{2}", bw, sw, gw);

                            }

                        }

                    }

                }

            }

            Console.WriteLine("一共有{0}个", count);

        }

        #endregion

        #region//12?56? * 123 = 154?4987

        static void Test3()

        {

            for (int a = ; a < ; a++)

            {

                for (int b = ; b < ; b++)

                {

                    for (int c = ; c < ; c++)

                    {

                        if (( + a + b * ) *  ==  + c * )

                        {

                            Console.WriteLine(a);

                            Console.WriteLine(b);

                            Console.WriteLine(c);

                        }

                    }

                }

            }

        }

        #endregion

        #region//1 1 2 3 5 8 13 21 34...递归计算第30位数

        static int Test4(int i)

        {

            if (i <= )

            {

                return ;

            }

            else if (i >  && i <= )

            {

                return ;

            }

            else

            {

                return Test4(i - ) + Test4(i - );

            }

        }

        #endregion

        #region//字符串反转

        static string Test5()

        {

            string s = "I am a good man";

            string[] arr = s.Split(' ');

            string res = "";

            for (int i = arr.Length - ; i >= ; i--)

            {

                res += arr[i];

                if (i > )

                    res += " ";

            }

            return res;

        }

        #endregion

        #region//九九乘法表

        static void Test6()

        {

            string t = string.Empty;

            for (int i = ; i < ; i++)

            {

                for (int j = ; j <= i; j++)

                {

                    t = string.Format("{0}*{1}={2} ", j, i, (j * i));

                    Console.Write(t);

                    if (i == j)

                        Console.Write("\n");

                }

            }

        }

        #endregion

        #region//冒泡排序 把一组数据按照从大到小/降序或从小到大/升序排列

        static void Test7()

        {

            int[] nums = { , , , , , , , , ,  };

            for (int i = ; i < nums.Length - ; i++)

            {

                for (int j = ; j < nums.Length -  - i; j++)

                {

                    if (nums[j] > nums[j + ])

                    {

                        int temp = nums[j];

                        nums[j] = nums[j + ];                    //Array.Sort(nums);//升序

                        nums[j + ] = temp;                       //Array.Reverse(nums);//反转

                    }

                }

            }

            for (int i = ; i < nums.Length; i++)

            {

                Console.Write(nums[i]);

            }

        }

        #endregion

    }

}