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Thread: First string is a substring of another

  1. #1
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    Default First string is a substring of another

    I need to write a User Defined Method which
    Checks if the first string is a substring of the second one.
    - Returns 0 if it is not a substring / 1 if it is / -1 if it is a “circular substring”
    this is an example of what it should do

    - abcde is a substring of blkjabcdelkjsd  return 1
    - abcde is not a substring of slfkjsdlskggfhjkh  return 0
    - abcde is a “circular substring” of delkjlkjabc  return -1

    Can Anyone help?

    All I have is
    public static int substring(String Str1, String Str2)
     {
       index1 = Str2.indexOf(Str1) 
     
     if (index1 >= 0)
     {
      return 1;
     else
     
     }
    Last edited by helloworld922; October 19th, 2009 at 07:52 PM.


  2. #2
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    Default Re: First string is a substring of another

    Here's a simple algorithm to check if a substring is contained within another string:

    1. start from the beginning of the larger string
    2. If the remaining characters is greater than the length of the second string, do 2a. Otherwise, do 2b
    2a. Use the substring() method of the String class to take a chunk that has the same length as the smaller string
    2b. Use the substring() method to take the rest of the letters in the larger string, then add on the remaining characters needed from the beginning
    3. compare if they are equal using the equals() method. If they are equal, return 1 or -1, depending on whether you used 2a or 2b. Otherwise, repeat 2-3 up to the last character in the larger string
    4. If you still haven't found a substring match, return 0.

  3. #3
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    Default Re: First string is a substring of another

    public static int substring(String Str1, String Str2)
     {
     int return = 0 
     for(int i = 0; i < Str2.length(); i++)
     {
       if (Str2.charAt(i) == Str1.charAt(0))
               for(int j =0; j < Str2.length(); j++) 
                  {
               if (Str2.charAt(i) == Str1.charAt(j))
     
                 return = 1;
               else 
                 return = 0;
       }
     }
     for(int i = 0; i < Str2.length(); i++)
     {
       if (i = Str2.length())
           i = 0
         for (int j = 0; j < Str2.length(); j++)
     
         return -1;
     }
    }
    }

    this is the code that I came up with for this problem can anyone see any errors with it
    if so please help me out in pinpointing them out
    Last edited by helloworld922; October 19th, 2009 at 10:33 PM.

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    Default Re: First string is a substring of another

    You're return statements are pre-mature. The program hasn't completely checked that the string is contained str2 is a substring of str1, but you're saying it is. Also, return is a Java keyword. You can't declare variables called return. There are a few other Java syntax errors (missing semi-colons).

  5. #5
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    Default Re: First string is a substring of another

    I know I was noticing that about the return statements also

    what would be your suggestions to make sure that the program completely checks that str2 is a substring of str1

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    Default Re: First string is a substring of another

    is this thread already solved?

  7. #7
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    Default Re: First string is a substring of another

    public static int substring(String str1, String str2)
    {
         for (int i = 0; i+str2.length() < str1.length(); i++)
         {
              if (str2.equals(str1.substring(i,i+str2.length()))
              {
                   return 1;
              }
         }
         for (int i = str1.length()-str2.length(); i< str1.length(; i++)
         {
              if (str2.equals(str1.substring(i,str1.length)+str1.substring(0,str2.length-i)))
              {
                   return -1;
              }
         }
         return 0;
    }

    Give this a go.

  8. The Following User Says Thank You to helloworld922 For This Useful Post:

    mgutierrez19 (October 20th, 2009)

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    Default Re: First string is a substring of another

    tnx hellowolrd... im trying to solve this one.. but im having hard time thinking of how.... hehe

  10. The Following User Says Thank You to chronoz13 For This Useful Post:

    mgutierrez19 (October 20th, 2009)

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    Default Re: First string is a substring of another

    Thank you guys very much for all you help

  12. #10
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    Default Re: First string is a substring of another

     for (int i = str1.length() - str2.length(); i < str1.length(); i++) {    
     
     if (str2.equals(str1.substring(i, str1.length() + str1.substring(0, str2.length() - i))))      //cannot find symbol  
       {           
        System.out.println("No Its Not!");        
      }


    Symbol: method subtring(int, java.lang.String)

  13. #11
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    Default Re: First string is a substring of another

    you're missing a closing parenthesis

    str2.equals(str1.substring(i, str1.length()[b])[/b] + str1.substring(0, str2.length() - i)))

  14. #12
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    Default Re: First string is a substring of another

    ahh hehehe

  15. #13
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    Default Substring

    - Checks if the first string is a substring of the second one.
    - Returns 0 if it is not a substring / 1 if it is / -1 if it is a “circular substring” (see example).

    Example:
    - abcde is a substring of blkjabcdelkjsd  return 1
    - abcde is not a substring of slfkjsdlskggfhjkh  return 0
    - abcde is a “circular substring” of delkjlkjabc  return -1

    I had already posted this method before but the last part where it is suppose to check for the circular substring does not seem to be running correctly, can someone look over it and see where i have to make correction on it im not sure if its even right

    public static int subVirus(String Str1, String Str2)
    	{
    		int result = 0;
     		for(int i = 0; i < Str2.length(); i++)
     		{
       			if (Str2.charAt(i) == Str1.charAt(0))
               			for(int j = (i + 1); j < Str2.length(); j++) 
                  			{
               				if (Str2.charAt(j) == Str1.charAt(j))
                 					result = 1;
       				}
     		}
     	                                   for(int i = 0; i < Str2.length(); i++)
                                               {
                                                    if (i = Str2.length())
                                                         i = 0
                                                        for (int j = 0; j < Str2.length(); j++)
     
                                                                 return = -1
                         }
     
    		return result;
    	}

  16. #14
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    Default Re: First string is a substring of another

    subVirus? I merged your two topics and marked the original one as un-solved.

    Oops, made a few logical errors in my solution a few posts back.

    	public static int substring(String str1, String str2)
    	{
    		if (str2.length() > str1.length())
    		{
    			return 0;
    		}
    		for (int i = 0; i + str2.length() <= str1.length(); i++)
    		{
    			if (str2.equals(str1.substring(i, i + str2.length())))
    			{
    				return 1;
    			}
    		}
    		for (int i = str1.length() - str2.length() + 1; i < str1.length(); i++)
    		{
    			if (str2.equals(str1.substring(i, str1.length()) + str1.substring(
    					0, i - str2.length() + str1.length())))
    			{
    				return -1;
    			}
    		}
    		return 0;
    	}

  17. The Following 2 Users Say Thank You to helloworld922 For This Useful Post:

    chronoz13 (October 22nd, 2009), mgutierrez19 (October 21st, 2009)

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