Question

My code is not giving me the right output. It reads numbers from a text file, converts them to an integer value and performs some multiplication on them. But the the products that method findProduct() gives me are wrong, so I think I am using the Integer.parseInt() method incorrectly.

I guess what is throwing me off is that It is trying to tell me the product of 96086×67017=2144428166, When checking on my calculator it is around 643939395462.

/*
 * 
 * Find the greatest product of five consecutive digits in the 1000-digit number.

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

this text file is in Project_8.txt
*/


import java.io.*;
// Import the scanner class that is used for reading the text file
import java.util.*;


public class Project_8 {

// Data members================================
// Object used to read the text file
private Scanner scanner;



// Public Methods==============================
// Points the scaaner object in the direction of the text file. Outputs an error if file is not found
public void openFile(){

    try{
        // Note the whole file's path is required
        scanner = new Scanner(new File("/Users/nicolematthews/Desktop/Tim/Java WORKSPACE/Project_Euler/src/Project_8.txt"));

    }catch(Exception e){

        System.out.println("Could not find the File. Check file's address");

    }
}



public String readFile(){

    // Instantiating the scanner for user input ruins its application for reading files
    //scanner = new Scanner(System.in);

    // Method looks the text file and adds each line of the text to the String sequence.
    // the Method returns sequence

        String sequence = "";

        // While the scanner has more data to read
        while(scanner.hasNext()){

            sequence = sequence + scanner.next();

        }

    return sequence;
}





// This method simply closes the scanner object
public void closeFile(){

    scanner.close();
}









public int findProduct(String sequence){


    int highestProduct = 0;

    for(int i = 0; i < ( sequence.length() - 10 ); i++){

        // Extract adjacent 5 digit strings which will be converted to integers
        String num1 = sequence.substring(i, i + 5);

        String num2 = sequence.substring(i + 5, i + 10);

        if( Integer.parseInt(num1)*Integer.parseInt(num2) > highestProduct ){

            highestProduct = Integer.parseInt(num1)*Integer.parseInt(num2);

            System.out.println(num1);
            System.out.println(num2);
            System.out.println(highestProduct);
            System.out.println("\n");

        }

    }

    return highestProduct;

}



// Main Method =========================================
public static void main(String args[] ) throws IOException{



    Project_8 object = new Project_8();

    object.openFile();

    String Sequence = object.readFile();

    System.out.println(Sequence);


    System.out.printf("%d Is the highest product of five consecutive \n" +
            "digits in the 1000-digit number.", object.findProduct(Sequence));



    // Finally, close the file when we are done with it.
            object.closeFile();
    /* Find the greatest product of five consecutive digits in the 1000-digit number


    System.out.println(Sequence);

*/      





}
}

Answer 1

Your sequence index i is only advancing by 1 for each iteration, i++, but you consume 10 characters on each iteration. You’ve indicated that this is your intent.

You’ll overflow a java int with many of the 5-digit sub-sequences from your data. For instance, your second product will be 31671 * 76531 = 2423813301. This is larget than Integer.MAX_INT: 2^31 – 1.

Changing the findProduct method to use long and Long.parseLong() will fix this.