how to convert null coefficients for the variables in equations "x^2+x^2+2x-x-25" to be "+1x^2+1x^2+2x-1x-25"?

Question

This is my attempting to fix the coefficient of any math equation variable for sum coefficients of the same variables like "x^2+x^2+2x-x-25" to be "+1x^2+1x^2+2x-1x-25" and then make the summation to be "2x^2+x-25", Notice that i have done the summation process in another method.

private static String fixCoeff(String equ)
{
    equ=equ.toLowerCase();//change equation variables to lower case
    equ=equ.trim();//remove white spaces
    String []characters={"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};
    int index=-1;
    String fixedCoeff="";
    for (int i = 0; i < characters.length; i++)
    {
        if(!equ.contains(characters[i]))
        {
            continue;
        }
        //if a not found in equ i++ 
        //if true execute this
        while(equ.indexOf(characters[i],++index)!=-1)
        {


            index=equ.indexOf(characters[i]);
            if(index==0)
            {
                fixedCoeff+="+1"+equ;
                equ=fixedCoeff;
                index=2;
                break;

            }
            else
            {

                if (equ.charAt(index-1)=='+'||equ.charAt(index-1)=='-')
                {
                    fixedCoeff=equ.substring(-1,index-1);
                    fixedCoeff+="1"+equ.substring(index-1,equ.length()-1);
                    equ=fixedCoeff;
                    index++;
                    break;
                }

            }

        //  if (index==equ.length()-1) {//if we found last element in equ is a variable
                //break;
            //}
        }//end while

    }//end for loop 


    return equ;

}//end fixCoeff

input cases :

a
x
x^2
x^2+x^2

output cases :

+1a
+1x
+1x^2
+1x^2+1x^2

What does your code output? It's easier to answer your question if you tell us what's happening. — CubeJockey, May 22 '15 at 15:06
@user1854282 check out my answer it accomplishes what you want with fewer lines of code. — brso05, May 22 '15 at 15:16
@user1854282 isn't output case 4 wrong? shouldn't it be +1x^2 + 1x^2? — nafas, May 22 '15 at 15:25

nafas · Accepted Answer · 2015-05-22T15:24:13.140

2

just to add up to @brso05 answer,

it is another way of doing this:

    String s ="x^2+x^2+2x-x-25";
    s=s.replaceAll("(?<!\\d)([a-z])", "1$1");    // <-- replaces any lower letters with 1 concatanted with the same letter
    if(!s.startsWith("-")){
        s="+"+s;  //<-- if the first character is not negative add a + to it.
    }
    System.out.println(s);

output:

+1x^2+1x^2+2x-1x-25

edited May 22 '15 at 15:24

answered May 22 '15 at 15:19

nafas

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nice no loop! I like it – brso05 May 22 '15 at 15:26

brso05 · Answer 2 · 2015-05-22T15:23:45.383

You can do this much easier using String.replaceAll() like this:

for (int i = 0; i < characters.length; i++)
{
    if(!equ.contains(characters[i]))
    {
        continue;
    }
    equ = equ.replaceAll(("(?<!\\d)" + characters[i]), ("1" + characters[i]));
}
if(!equ.startsWith("-") && !equ.startsWith("+"))
{
    equ = "+" + equ;
}

This will replace the character where there is no digit in front of it with 1x(or whatever the current character is). This uses regex with a negative lookbehind to make sure there are no digits in front of the character then it will replace with 1(character).

Here is a self-contained example:

String line = "x-x^2+3x^3";
line = line.replaceAll("(?<!\\d)x", "1x");
System.out.println("" + line);

This will output 1x-1x^2+3x^3.

how to convert null coefficients for the variables in equations "x^2+x^2+2x-x-25" to be "+1x^2+1x^2+2x-1x-25"?

2 Answers2