Project Euler N# 8 JAVA

Question

I am trying to solve this problem and I think I am in the right track but for some reason the program does not run in a specific condition. This is the code:

public class Eight {
    public static void main(String[] args) {
        String set = "731671765313306249192251196744265747423"
                + "553491949349698352031277450632623957831801698"
                + "480186947885184385861560789112949495459501737958"
                + "331952853208805511125406987471585238630507156932909"
                + "632952274430435576689664895044524452316173185640309871"
                + "112172238311362229893423380308135336276614282806444486645"
                + "238749303589072962904915604407723907138105158593079608"
                + "66701724271218839987979087922749219016997208880937"
                + "7665727333001053367881220235421809751254540594752"
                + "243525849077116705560136048395864467063244157221"
                + "55397536978179778461740649551492908625693219784"
                + "686224828397224137565705605749026140797296865"
                + "241453510047482166370484403199890008895243450"
                + "6585412275886668811642717147992444292823086346567481391912316282458617866458"
                + "3591245665294765456828489128831426076900422421902267105562632111110937054421750694165"
                + "8960408071984038509624554443629812309878799272442849091888458015616609791913387549920052"
                + "4063689912560717606058861164671094050775410022569831552000559357297257163626956188267042"
                + "8252483600823257530420752963450";

        int initialIndex = 0;
        int lastIndex = 4;
        int finale = 0;

        for (;last <= set.length() - 1; initialIndex++, lastIndex++)
        {
            int num = Integer.parseInt(set.substring(initialIndex, lastIndex));
            int result = 1;

            while (num > 0)
            { 
                int digit = num % 10;
                result *= digit;
                num /= 10;
            }

            if (result > finale) 
                finale = result;
        } //end for 

        System.out.println(finale);
    }
}

When lastIndex equals 4, the result I get is 5832, which is the same result as Project Euler gives you as an example. But when Im trying to run this program with 13 numbers instead of 4, I get an exception and the program does not run.

Answer 1

Your issue begins here:

            int num = Integer.parseInt(set.substring(initialIndex, lastIndex));

When you set lastIndex as 13, the number you are trying to take out of the string is 7,316,717,653,133. In your code, you are trying to parse that String as an int, which has a maximum value of 2^31 2,147,483,647.

You can fix your problem by making any variable you expect to excede 2^31 a different integral data type, like a long.

Answer 2

A 13 digit string will exceed the maximum allowable size of an int. Use Long.parseLong and change num from int to long. I did it, and got the following when I used 13 digits: 2091059712