Java Recursion return

Question

so there was a problem I had in implementing a program (given below). The problem occurs when I pass num = 1006, the private method returns "MVI", but the public method returns "M". Could anyone explain this?

public class Solution {
    public String intToRoman(int num) {
       String j = intToRoman(num, "");
       return j;
    }

private String intToRoman(int num, String s) {
    //String s = "";
    if (num >= 1000) {
        s += 'M';
        num -= 1000;
        intToRoman(num, s);
    } else if (num >= 500) {
        s += 'D';
        num -= 500;
        intToRoman(num, s);
    } else if (num >= 100) {
        s += 'C';
        num -= 100;
        intToRoman(num, s);
    } else if (num >= 50) {
        s += 'L';
        num -= 50;
        intToRoman(num, s);
    } else if (num >= 10) {
        s += 'X';
        num -= 10;
        intToRoman(num, s);
    } else if (num >= 5) {
        s += 'V';
        num -= 5;
        System.out.println("Checkpoint 1");
        System.out.println(s);
        intToRoman(num, s);
    } else if (num >= 1) {
        s += 'I';
        num -= 1;
        System.out.println("Checkpoint 2");
        intToRoman(num, s);
    } else {
        System.out.println("Returning "+ s);
        return s;
    }
    return s;
}

You might want to return intToRomain(num, s);.

Andy Turner
– Andy Turner

2016-11-09 08:25:37 +00:00
Commented Nov 9, 2016 at 8:25 — Andy Turner
– Andy Turner, Commented Nov 9, 2016 at 8:25
use StringBuilder if you don't want re-assigned value s

Viet
– Viet

2016-11-09 08:37:54 +00:00
Commented Nov 9, 2016 at 8:37 — Viet
– Viet, Commented Nov 9, 2016 at 8:37

Eran · Accepted Answer · 2016-11-09 08:27:47Z

2

intToRoman(num, s) doesn't change the value of s, since Java is a pass by value language.

You should replace each

intToRoman(num, s);

with

s = intToRoman(num, s);

in order for s to be assigned a new value.

The alternative is to return intToRoman(num, s) instead of s.

answered Nov 9, 2016 at 8:27

Eran

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