prefix to infix notation using an recursive algorithm

Question

I am new here and I am somehow stuck. I created an recursive algorithm that uses an global variable for remembering the Position he made the recursive call and I am trying to get rid of this variable as for me it seems to be not a good solution.

Is there any chance to get rid of this global variable? I cannot adjust the method-head so therefore the Interface of the method is fixed.

Here you can see my Code:

static int pos = -1;
static boolean writeInfix(char[] expr) {
    boolean result;
    pos++;
    int printpos = pos;
    if(expr[pos]=='+'||expr[pos]=='-'||expr[pos]=='/'||expr[pos]=='*'){
        System.out.print("(");
        writeInfix(expr);
        System.out.print(expr[printpos]);
        result = writeInfix(expr);
        System.out.print(")");
        return result;
    }else if(expr[pos] >= 'a' && expr[pos] <= 'z'){
        System.out.print(expr[pos]);
        return true;
    }else{
        return false;
    }
}

Thank you for your help :)

Thank you for your help! :)

Skloli
– Skloli

2017-05-26 15:59:23 +00:00
Commented May 26, 2017 at 15:59 — Skloli
– Skloli, Commented May 26, 2017 at 15:59

amit · Accepted Answer · 2017-05-26 15:50:57Z

2

You can add a new auxiliary method, where you control its variables, and let writeInfix(char[]) be only a wrapper, that does nothing but calling the "real" method.

In this new method, pos is an arument.

This also ensures you can call your API method (writeInfix) twice (independently) without worrying from the side effects (pos is initialized with wrong value after first call).

edited May 26, 2017 at 15:50

answered May 26, 2017 at 9:15

amit

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Comments

QBrute · Accepted Answer · 2017-05-26 09:19:13Z

You should be able to write another method with the position as additional argument:

private static boolean writeInfix(char[] expr, int pos) {
    boolean result;
    int printpos = pos;
    if(expr[pos]=='+'||expr[pos]=='-'||expr[pos]=='/'||expr[pos]=='*'){
        System.out.print("(");
        writeInfix(expr);
        System.out.print(expr[printpos]);
        result = writeInfix(expr, pos + 1);
        System.out.print(")");
        return result;
    }else if(expr[pos] >= 'a' && expr[pos] <= 'z'){
        System.out.print(expr[pos]);
        return true;
    }else{
        return false;
    }
}

and in the method you already have, you just need to call

static boolean writeInfix(char[] expr) {
    return writeInfix(expr, -1);
}

pkgajulapalli · Accepted Answer · 2017-05-26 09:19:41Z

0

You can add pos as an argument to the writeInfix function.

static boolean writeInfix(char[] expr, int pos);

Whereever you are returning false, return -1. Whereever you are returning true, return the current pos value.

answered May 26, 2017 at 9:19

pkgajulapalli

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