project-euler/LargestProductInASeries.java

/* The four adjacent digits in the 1000-digit number that have the greatest
product are 9 × 9 × 8 × 9 = 5832.

7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450

Find the thirteen adjacent digits in the 1000-digit number that have the
greatest product. What is the value of this product? */

// To get a slice of the array of numbers
import java.util.Arrays;
/* To ensure that all numbers are processed, even if the amount of numbers left
in the array is less than the slice size */
import java.lang.ArrayIndexOutOfBoundsException;

public class LargestProductInASeries {
  /* To create an array of characters that can be split into slices, based on
  the number of numbers to be multiplied together */
  private String numString = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";

  // To store each number in the string as a separate element in an array
  private char[] nums;

  public LargestProductInASeries() {
    this.nums = numString.toCharArray();
  }

  /* "num" parameter is used to specify the size of each slice of the provided
  number */
  public int findGreatestProduct(int num) {
    // To contain the largest product of the specified subset of all the numbers
    int largestProduct = 0;
    // To contain each subset of numbers to be multiplied together
    char[] slice;
    // To get the product for each slice of the array
    int product;

    for (int i = 0; i < this.nums.length; i++) {
      // To make sure the product for each slice only has that slice's data
      product = 0;

      if ( !((i + num) >= this.nums.length - 1) ) {
        slice = Arrays.copyOfRange(this.nums, i, i + num);
        System.out.println(slice);
        // To multiply all the numbers on the specified slice together
        for (char character : slice) {
          int charNum = Character.getNumericValue(character);
          if (product == 0) {
            product = charNum;
          } else {
            product *= charNum;
          }
        }
        /* To determine if the current product is greater than the current
        largest product */
        if (product > largestProduct)
          largestProduct = product;
      }
    }
    return largestProduct;
  }
}