Ian Limarta - 4 months ago 15

Java Question

I'm working on solving an equation but I will like to use the constants to program my solution.

The method I'm working on is called decompose which decomposes the equation into constants. The problem is that when I split, an equation with a negative constant will yield an array with the absolute value of the constants. How can I achieve the minus sign while still using regex?

If the input is

`ax+by=c`

`{a,b,c}`

Helpful bonus: Is there a way to delete the empty elements that is created when I split. For example, if I type equation

`2x+3y=6`

`{2,,3,,6}`

Code:

`public static int[] decompose(String s)`

{

s = s.replaceAll(" ", "");

String[] termRaw = s.split("\\D"); //Splits the equation into constants *and* empty spaces.

ArrayList<Integer> constants = new ArrayList<Integer>(); //Values are placed into here if they are integers.

for(int k = 0 ; k < termRaw.length ; k++)

{

if(!(termRaw[k].equals("")))

{

constants.add(Integer.parseInt(termRaw[k]));

}

}

int[] ans = new int[constants.size()];

for(int k = 0 ; k < constants.size(); k++) //ArrayList to int[]

{

ans[k] = constants.get(k);

}

return ans;

}

Answer

The general strategy to this answer is to split the input equation by operator, then extract out the coefficients in a loop. However, there are several edge cases which need to be considered:

- a plus symbol (
`+`

) is prefixed to every minus which does not appear either as the first term - after splitting, a coefficient of positive one is detected by seeing empty string
- after splitting, a coefficient of negative one is detected by seeing a minus sign

```
String input = "-22x-77y+z=-88-10+33z-q";
input = input.replaceAll(" ", "") // remove whitespace
.replaceAll("=-", "-"); // remove equals sign
.replaceAll("(?<!^)-", "+-"); // replace - with +-, except at start of line
// input = -22x+-77y+z+-88+-10+33z+-
String[] termRaw = bozo.split("[\\+*/=]");
// termRaw contains [-22x, -77y, z, -88, -10, 33z, -]
ArrayList<Integer> constants = new ArrayList<Integer>();
for (int k=0 ; k < termRaw.length ; k++) {
termRaw[k] = termRaw[k].replaceAll("[a-zA-Z]", "");
if (termRaw[k].equals("")) {
constants.add(1);
}
else if (termRaw[k].equals("-")) {
constants.add(-1);
}
else {
constants.add(Integer.parseInt(termRaw[k]));
}
}
```