I'm a beginner in C# and I'm stuck at this problem.

  string original = "foo bar foo $ bar $ foo bar $ ";  
  string desired_output = "foo bar foo $ bar foo bar";  

I found a rough code but the result is not good.

Can you help me solve the problem?

Here is my code:

  string s = "foo bar foo $ bar $ foo bar $ ";

  char ch = '$';

  for (int i = 0; i < s.Length; i  )
  {
      if (s[i] == ch)
      {
          s = s.Substring(0, i)  
          s.Substring(i   1);
          break;
      }
   }
   
   for (int i = s.Length - 1; i > -1; i--)
   {            
       if (s[i] == ch)
       {
           s = s.Substring(0, i)  
           s.Substring(i   1);
           break;
       }
   }
   Console.WriteLine(s);
   

The output I receive is foo bar foo bar $ foo bar.

CodePudding user response：

string original = "foo bar foo $ bar $ foo bar $ "; 
string desired_output = "foo bar foo $ bar foo bar"; 

string result = original; 
int index = original.IndexOf("$") 1;    
if (index > 0) 
{
    result = (original.Substring(0, index)    original.Substring(index).Replace("$", "")).Replace("  ", " ").Trim();
}

Console.WriteLine(desired_output == result);

See it here:

https://dotnetfiddle.net/I3lVua

Or:

string original = "foo bar foo $ bar $ foo bar $ "; 
string desired_output = "foo bar foo $ bar foo bar"; 

var buffer = original.ToCharArray();
bool found = false;
int dest = 0;
for(int i = 0; i < buffer.Length; i  )
{
    if (buffer[i] != '$' || !found)
    {
       buffer[dest] = buffer[i];
       dest  ;
    }
    if (buffer[i] == '$') found = true;
}

var result = new string(buffer, 0, dest).Replace("  ", " ").Trim();
    
Console.WriteLine(desired_output == result);

https://dotnetfiddle.net/iVtw8E

Notice for both solutions there is an issue with the extra spacing, hence the extra Replace() and Trim() calls.

CodePudding user response：

If you want to keep only the first $ then the first thing you would need to do is use that first for loop to find the first $ and make the latter substring until the end of the main string. Once you've done that, use the Replace function to replace all other $ in that substring. Then just combine the first part of the substring and the cleaned second part and you will get your desired output

CodePudding user response：

You do not need 2 for loops for that. One is enough. Just copy all chars into a StringBuilder, except, if the char is the desired character ($) and it was already copied once before. A single bool flag suffices to accomplish that.

using System;
using System.Text;

namespace cs
{
    class Program
    {
        static string RemoveAllButFirst(char c, string s) {
            var first = true;
            var sb = new StringBuilder();
            foreach (char x in s) {
                if (c == x) {
                    if (first) {
                        sb.Append(x);
                        first = false;
                    }
                } else {
                    sb.Append(x);
                }
            }
            return sb.ToString();
        }
    
        static void Main(string[] args)
        {
            string original = "foo bar foo $ bar $ foo bar $ ";
            System.Console.WriteLine(original);
            System.Console.WriteLine(RemoveAllButFirst( '$', original));
        }
    }
}