Programming Forums > Application Development > C#

allenm · Nov 9th, 2005, 12:03 PM

Hello, I am presented with the following problem and have tried desperately (over 12 hours) to solve it:

I have a string say "011010101" and I want to parse this string based on a table of values:

i = 0
m = 011
k = 10
e = 101

I want to construct an algorithm that will go through the string above and parse it assigning each value to their corresponding table value. Looking at it, I know that the string would become "011" , "0" , "10" , "101" which for this example would be "mike" in that order. Since "i" is the first thing I check, my code tries to form "0", "11010101", and nothing else will get extracted. There can be more than one correct parsing and also the table of values includes all the letters (uppercase and lowercase) as well as ' ', '\n', and '\t'. Any help would be greatly appreciated.

MBirchmeier · Nov 9th, 2005, 12:57 PM

Quote:

Originally Posted by allenm

There can be more than one correct parsing and also the table of values includes all the letters (uppercase and lowercase) as well as ' ', '\n', and '\t'. Any help would be greatly appreciated.

Posting what you've tried so far would also be appreciated. That way we can help and not give

Polyphemus_ · Nov 9th, 2005, 1:05 PM

Google for bitshifting, you'll probably find some tuts.

allenm · Nov 9th, 2005, 1:15 PM

(Toggle Plain Text)

string ConvertCodes( string binary )
{
 // what to return
 string retval = "";
 
 // what to restore the passed in value to just incase
 string tempCopy = binary;
 
 foreach( PairItem i in CodeList )
 {
    // if the CODE (i.e. "011") is a prefix of the passed in string
    if( binary.StartsWith( i.CODE ) )
    {
      // add the symbol (i.e. "i") to the return value string
      retval+=i.Symbol.ToString();
     
      // update the passed in string for further checking
      binary = binary.SubString( i.CODE.Length );
      
      // check the update string, if it equals "", there were no further matches
      if( ConvertCodes(binary) == "" )
      {
        // reset the return value
        retval = "";

        // restore the passed in string
        binary = tempCopy;
      }
    }
 }

 return retval
}

I ran through this code in debug mode for a simple string, and it found the correct return value, but it still returned "".

MBirchmeier · Nov 9th, 2005, 1:27 PM

Quote:

Originally Posted by allenm

(Toggle Plain Text)

string ConvertCodes( string binary )
{
 // what to return
 string retval = "";
 
 // what to restore the passed in value to just incase
 string tempCopy = binary;
 
 foreach( PairItem i in CodeList )
 {
    // if the CODE (i.e. "011") is a prefix of the passed in string
    if( binary.StartsWith( i.CODE ) )
    {
      // add the symbol (i.e. "i") to the return value string
      retval+=i.Symbol.ToString();
     
      // update the passed in string for further checking
      binary = binary.SubString( i.CODE.Length );
      
      // check the update string, if it equals "", there were no further matches
      if( ConvertCodes(binary) == "" )
      {
        // reset the return value
        retval = "";

        // restore the passed in string
        binary = tempCopy;
      }
    }
 }

 return retval
}

I ran through this code in debug mode for a simple string, and it found the correct return value, but it still returned "".

Well the good news is you're close...

Look closer at your termination case, what's returned by :
ConvertCodes("") ; // (should be "")

now what's returned by
ConvertCodes("011");

hint:

(Toggle Plain Text)

      if( ConvertCodes(binary) == "" )
      {
        // reset the return value
        retval = "";

        // restore the passed in string
        binary = tempCopy;
      }

That should help out with one character 'strings'.

Once you get that, you also have no ability to create multi character strings. You're never getting/saving / returning information from characters after the first.

-MBirchmeier
(feel free to ask questions)

allenm · Nov 9th, 2005, 1:44 PM

I ran my code with those two values and I got the same return value. I know this is because when I get done with the algorithm, no matter what, at some point ConverCodes(binary) will equal "", so I return "" no matter what, even if I pass in one character string. How would I go about solving this?

MBirchmeier · Nov 9th, 2005, 1:58 PM

Quote:

Originally Posted by allenm

How would I go about solving this?

Well after you find your starting character there are three valid scenarios:

1.) You've reached the end of the string
2.) The rest of the string is a valid series of characters
3.) The rest of the string is not a valid series of characters

-MBirchmeier

Nov 9th, 2005, 12:03 PM	#1
allenm Newbie Join Date: Nov 2005 Posts: 3 Rep Power: 0	Algorithm Question - Urgent Help Needed Hello, I am presented with the following problem and have tried desperately (over 12 hours) to solve it: I have a string say "011010101" and I want to parse this string based on a table of values: i = 0 m = 011 k = 10 e = 101 I want to construct an algorithm that will go through the string above and parse it assigning each value to their corresponding table value. Looking at it, I know that the string would become "011" , "0" , "10" , "101" which for this example would be "mike" in that order. Since "i" is the first thing I check, my code tries to form "0", "11010101", and nothing else will get extracted. There can be more than one correct parsing and also the table of values includes all the letters (uppercase and lowercase) as well as ' ', '\n', and '\t'. Any help would be greatly appreciated.

Nov 9th, 2005, 1:15 PM	#4
allenm Newbie Join Date: Nov 2005 Posts: 3 Rep Power: 0	(Toggle Plain Text) string ConvertCodes( string binary ) { // what to return string retval = ""; // what to restore the passed in value to just incase string tempCopy = binary; foreach( PairItem i in CodeList ) { // if the CODE (i.e. "011") is a prefix of the passed in string if( binary.StartsWith( i.CODE ) ) { // add the symbol (i.e. "i") to the return value string retval+=i.Symbol.ToString(); // update the passed in string for further checking binary = binary.SubString( i.CODE.Length ); // check the update string, if it equals "", there were no further matches if( ConvertCodes(binary) == "" ) { // reset the return value retval = ""; // restore the passed in string binary = tempCopy; } } } return retval } string ConvertCodes( string binary ) { // what to return string retval = ""; // what to restore the passed in value to just incase string tempCopy = binary; foreach( PairItem i in CodeList ) { // if the CODE (i.e. "011") is a prefix of the passed in string if( binary.StartsWith( i.CODE ) ) { // add the symbol (i.e. "i") to the return value string retval+=i.Symbol.ToString(); // update the passed in string for further checking binary = binary.SubString( i.CODE.Length ); // check the update string, if it equals "", there were no further matches if( ConvertCodes(binary) == "" ) { // reset the return value retval = ""; // restore the passed in string binary = tempCopy; } } } return retval } I ran through this code in debug mode for a simple string, and it found the correct return value, but it still returned "".

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Nov 9th, 2005, 1:05 PM	#3
Polyphemus_ Expert Programmer Join Date: Aug 2005 Location: Rotterdam, the Netherlands Posts: 942 Rep Power: 4	Google for bitshifting, you'll probably find some tuts.

Nov 9th, 2005, 1:44 PM	#6
allenm Newbie Join Date: Nov 2005 Posts: 3 Rep Power: 0	I ran my code with those two values and I got the same return value. I know this is because when I get done with the algorithm, no matter what, at some point ConverCodes(binary) will equal "", so I return "" no matter what, even if I pass in one character string. How would I go about solving this?

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Programming Forums > Application Development > C#

Algorithm Question - Urgent Help Needed