C ＃ basic 4-written examination question 1

Fibonacci Series No n Number

1 1 2 3 5 8 13 Please n Number ？

The simplest recursion , The first two numbers return directly 1 , The next value is returned as the sum of the first two numbers

//  recursive  1 1 2 3 5 8 13
    static int GetNumber(int n)
    {
        int ret = 1;
        if (n > 2)
        {
            return GetNumber(n - 1) + GetNumber(n - 2);
        }
        else
        {
            return ret;
        }
    }

Replace the bottle cap with soda

altogether A Yuan Unit purchase price B Soft drink Every time C The lid of a bottle of soda can be exchanged for a bottle of soda How many bottles can I buy ？

Buy soda for the first time and get A/B bottle , The remaining caps A/B individual
For the second time, the bottle cap is not enough C individual , Cannot exchange ; The cap is enough , obtain A/B/C bottle , The remaining caps A/B/C One plus deficiency C Part of A/B%C

static int Buy(int a, int b, int c)
    {
        return a / b + Cap(c, a / b);
    }
    //  recursive   Every time  c  A lid for a bottle of soda   altogether  d  Covers   How much soda can I change ？
    static int Cap(int c, int d)
    {
        //  Not enough to exchange for a bottle of soda 
        if (d < c)
        {
            return 0;
        }
        else
        {
            //  Judge whether the subsequent covers can continue to be exchanged  d / c  It's the bottle I got this time  + d % c  Exchange the remaining bottle caps this time 
            return d / c + Cap(c, d / c + d % c);
        }
    }

Turn on the light

A row of lamps in total n individual , The first person turns on all the lights , The first 2 Personal close all the number 2 Multiple Lights , The first 3 Individuals open all the pages 3 Multiple Lights , The first k One person opens / Close all sections k Multiple , Which lights are finally turned on ？

	static void Main()
    {
        GetLight(100, 100);
    }
    static void GetLight(int n, int k)
    {
        //  The default is  false
        bool[] light = new bool[n];
        //  The first person starts to traverse 
        for (int i = 1; i <= k; i++)
        {
            //  The first light starts to operate 
            for (int j = 0; j < n; j++)
            {
                //  Operation No.  j  Lights  j  Exactly  i  Multiple 
                if ((j+1) % i == 0)
                {
                    light[j] = !light[j];
                }
            }
        }
        //  Print the results 
        for (int i = 0; i < n; i++)
        {
            if (light[i])
                Console.WriteLine(i+1);
        }
    }

Integer output is octal number output

	static void Main()
    {
        d2(10);
    }
    static void d2(int i)
    {
        if (i > 7)
        {
            d2(i / 8);
        }
        Console.Write(i % 8);
    }

Print 200 The prime number within

Prime number ： Can only be 1 And divide themselves

	static void Main()
    {
        GetNumber(200);
    }
    static void GetNumber(int num)
    {
        int count = 0;
        for (int i = 1; i <= num; i++)
        {
            for (int j = 2; j < i; j++)
            {
                if (i % j == 0 && i != j)
                {
                    break;
                }
                if (j == i - 1)
                {
                    count++;
                    Console.WriteLine(i);
                }
            }
        }
        Console.WriteLine("count:" + count);
    }

Yang hui triangle

Print 7 Row Yang Hui triangle number Use a two-dimensional array

		int[][] a = new int[7][];
        for (int i = 0; i < 7; i++)
        {
            a[i] = new int[i + 1];
            a[i][0] = 1;
            a[i][i] = 1;
            if (i > 1)// Find the intermediate data 
            {
                for (int j = 1; j < i; j++)
                {
                    //  Number of current intermediate index positions   be equal to   The sum of the number at the same index position of the previous row and the previous number 
                    a[i][j] = a[i - 1][j - 1] + a[i - 1][j];
                }

            }
        }
        //  Print 
        for (int i = 0; i < a.Length; i++)
        {
            for (int k = 0; k < a.Length - 1 - i; k++)
            {
                Console.Write(" ");
            }
            for (int j = 0; j < a[i].Length; j++)
            {
                Console.Write(string.Format("{0:00}", a[i][j]));
                if (j != a[i].Length - 1)
                {
                    Console.Write(" ");
                }
            }
            Console.WriteLine();
        }

The time problem of fishing for three days and drying nets for two days

Suppose the fisherman comes from 2022 year 6 month 1 The date of , Three days fishing and two days net drying , Today is fishing or drying nets ？

Console.WriteLine(DateTime.Now.Day - DateTime.Parse("2022-06-01").Day % 5 < 3 ? " Fishing " : " Basking net ");