/*
 * Problem description from Project Euler:
 *
 * The four adjacent digits in the 1000-digit number that have the
 * greatest product are 9 × 9 × 8 × 9 = 5832.
 *
 * 73167176531330624919225119674426574742355349194934
 * 96983520312774506326239578318016984801869478851843
 * 85861560789112949495459501737958331952853208805511
 * 12540698747158523863050715693290963295227443043557
 * 66896648950445244523161731856403098711121722383113
 * 62229893423380308135336276614282806444486645238749
 * 30358907296290491560440772390713810515859307960866
 * 70172427121883998797908792274921901699720888093776
 * 65727333001053367881220235421809751254540594752243
 * 52584907711670556013604839586446706324415722155397
 * 53697817977846174064955149290862569321978468622482
 * 83972241375657056057490261407972968652414535100474
 * 82166370484403199890008895243450658541227588666881
 * 16427171479924442928230863465674813919123162824586
 * 17866458359124566529476545682848912883142607690042
 * 24219022671055626321111109370544217506941658960408
 * 07198403850962455444362981230987879927244284909188
 * 84580156166097919133875499200524063689912560717606
 * 05886116467109405077541002256983155200055935729725
 * 71636269561882670428252483600823257530420752963450
 *
 * Find the thirteen adjacent digits in the 1000-digit number that
 * have the greatest product. What is the value of this product?
 */

import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.FileNotFoundException;

import java.util.ArrayList;
import java.util.List;

public class LargestProductInASeries {

  private static final int SEQUENCE_LENGTH = 13;
  private static final String FILENAME     = "008/input.txt";

  public static void main(String[] args) {
    List<Character> digits = charactersFromFromFile(new File(FILENAME));
    long max = 0;

    for (int startIndex = 0; startIndex < digits.size() - SEQUENCE_LENGTH; startIndex++) {
      int[] values = new int[SEQUENCE_LENGTH];

      // Read sub-sequence
      for (int i = 0; i < SEQUENCE_LENGTH; i++) {
        char digit = digits.get(i + startIndex);
        values[i]  = Character.getNumericValue(digit);

        // Skip past the '0' in list of digits
        if (digit == '0') {
          startIndex += i + 1;
          break;
        }
      }

      // Calculate product
      long product = productOfNumbers(values);
      max = product > max ? product : max;
    }

    System.out.println(max);
  }

  private static long productOfNumbers(int[] numbers) {
    long product = 1;
    for (int number : numbers) {
      product *= number;
    }
    return product;
  }

  private static List<Character> charactersFromFromFile(File file) {
    List<Character> characters = new ArrayList<>();

    try {
      FileReader fileReader = new FileReader(file);
      while (fileReader.ready()) {
        char input = (char)fileReader.read();
        if (input != '\n') {
          characters.add(input);
        }
      }
      fileReader.close();
    } catch (FileNotFoundException exception) {
      exception.printStackTrace();
    } catch (IOException exception) {
      exception.printStackTrace();
    }

    return characters;
  }
}