• I have to write a program that displays all the combinations of operators( and -), to put between numbers from 1 to N (N>=2), in order to reach a targeted value X. It should write "N/A" if there is no possibility.

For the input:

• n=6
• x=3

It displays:

• 1 2 3 - 4 - 5 6 = 3
• 1 2 - 3 4 5 - 6 = 3
• 1 - 2 - 3 - 4 5 6 = 3

using System;

namespace ConsoleApp1
{
    class Program
    {
       static bool counter;

       static void Generate(int n, int x, int currentIndex, int result, string expression)
        {
            counter = true;

            if (currentIndex == n   1)
            {
                if (result == x)
                {
                    Console.WriteLine(expression   " = "   x);
                }

                return;
            }

            Generate(n, x, currentIndex   1, result   currentIndex, expression   "   "   currentIndex);
            Generate(n, x, currentIndex   1, result - currentIndex, expression   " - "   currentIndex);
        }

       static void Main()
        {
            int n = Convert.ToInt32(Console.ReadLine());
            int x = Convert.ToInt32(Console.ReadLine());
            const int doi = 2;

            Generate(n, x, doi, 1, "1");

            if (!counter)
            {
                Console.WriteLine("N/A");
            }

            Console.ReadLine();
        }
    }
}

 It gives me the error : JRM003 (Error) : Don't use static fields. (line: 7, character: 7).

Where can I place the "counter" in order to track if there is possibility of reaching to the targeted value, and get rid of the error.

CodePudding user response：

The best thing to do is to use ref:

using System;

namespace ConsoleApp1
{
    class Program
    {
      
        static void Main(string[] args)
        {
            int n = Convert.ToInt32(Console.ReadLine());
            int x = Convert.ToInt32(Console.ReadLine());
            const int doi = 2;

            bool counter = false;
            Generate(n, x, doi, 1, "1", ref counter);

            if (!counter)
            {
                Console.WriteLine("N/A");
            }

            Console.ReadLine();
        }
        
        static void Generate(int n, int x, int currentIndex, int result, string expression, ref bool counter)
        {
            counter = true;

            if (currentIndex == n   1)
            {
                if (result == x)
                {
                    Console.WriteLine(expression   " = "   x);
                }

                return;
            }

            Generate(n, x, currentIndex   1, result   currentIndex, expression   "   "   currentIndex, ref counter);
            Generate(n, x, currentIndex   1, result - currentIndex, expression   " - "   currentIndex, ref counter);
        }
    }
}

CodePudding user response：

Here's how I'd do it. Count in binary treating 0 as subtraction and 1 as addition:

    public static void Main(string[] args)
    {
        int n, x;
        String response1, response2;

        Console.Write("Enter a value for 'n' [n>=2]: ");
        response1 = Console.ReadLine();
        Console.Write("Enter a value for 'x': ");
        response2 = Console.ReadLine();

        if (int.TryParse(response1, out n) && int.TryParse(response2, out x))
        {
            if (n >= 2)
            {
                List<String> solutions = new List<string>();
                int[] numbers = Enumerable.Range(1, n).ToArray();
                int width = numbers.Length - 1;
                int max = (int)Math.Pow(2, numbers.Length - 1);
                for(int i=0; i < max; i  )
                {
                    int sum = numbers[0];
                    String binary = Convert.ToString(i, 2).PadLeft(width, '0');
                    String equation = numbers[0].ToString();
                    for(int d=0; d<binary.Length; d  )
                    {
                        char operation = binary[d];
                        equation = equation   ((operation == '0') ? " - " : "   ")   numbers[d   1];
                        sum = sum   ((operation == '0') ? -1 : 1) * numbers[d   1];
                    }
                    equation = equation   " = "   sum;
                    if (sum == x)
                    {
                        solutions.Add(equation);
                    }
                }
                if (solutions.Count == 0)
                {
                    Console.WriteLine("N/A");
                }
                else
                {
                    foreach(String solution in solutions)
                    {
                        Console.WriteLine(solution);
                    }
                }
            }
            else
            {
                Console.WriteLine("'n' must be greater than or equal to 2.");
            }
        }
        else
        {
            Console.WriteLine("Invalid value for 'n' or 'x'!");
        }

        Console.WriteLine("Press Enter to Quit.");
        Console.ReadLine();
    }

Output:

Enter a value for 'n' [n>=2]: 6
Enter a value for 'x': 3
1 - 2 - 3 - 4   5   6 = 3
1   2 - 3   4   5 - 6 = 3
1   2   3 - 4 - 5   6 = 3
Press Enter to Quit.