(Yet Another) UVa 3n+1 Help Question

Question

Hi,

I have been beating my head against the wall trying to figure out why this is returning "Wrong Answer." I'd greatly appreciate any feedback.

Edit: I reposted the code, and this version finally fixed the "Runtime Error" by allowing for multiple spaces between the number pair. It now is saying "Wrong Answer" but as far as I can tell, I copied the given algorithm verbatim, so I'm at a loss.

Thanks.

The Problem

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;


public class Main {

public static void main(String[] args) {
   Main mine = new Main();
   mine.begin();
}

public void begin(){
    BufferedReader sys = new BufferedReader(new InputStreamReader(System.in));
    String[] pair;
    try{
        while((pair=sys.readLine().split(" +")).length==2){
            System.out.println(pair[0]+ " " +pair[1] + " " + getMax(Integer.parseInt(pair[0]),Integer.parseInt(pair[1])));
        }
    }catch(IOException ex){
        return;
    }
}

private String getMax(int a, int b){
    int maxcount,thiscount, num, n;

    for(maxcount = -1, num =Math.min(a, b); num <= Math.max(a, b); num++ ){
        for(n = num, thiscount = 1; n!=1; thiscount++){
            if(n%2==0)n=n/2;
            else n = 3*n +1;
        }
        if(thiscount>maxcount) maxcount = thiscount;
    }
    return String.valueOf(maxcount);
}
}

Answer 1

while(num<4){
...

Is the input always limited to 4 lines?

Answer 2

You might want to reconsider how you parse the lines. I believe the only lines that could have runtime errors in your code are the integer parsing ones. You're assuming that each i and j are separated by a single space. The question makes no mention of how much whitespace will be on a line.

Answer 3

If you're getting a wrong answer, and your program works on the samples, then the problem is probably tied to the fact that you're using ints rather then longs.

For the 3n+1 problem, the intermediate values can grow to be larger then an int can handle (2,147,483,647), and it's a common way for judge data to be evil.