Problem008.java

/**
 * Problem 8:
 * The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
 * Find the thirteen adjacent digits in the 1000-digit number that have the greatest product.
 * What is the value of this product?
 */
public class Problem008 {

    private static long greatestProduct(String number, int adjacentDigits) {
        long greatest = 0;
        for (int i=0; i<=number.length()-adjacentDigits; i++) {
            long p = number
                    .substring(i, i+adjacentDigits)
                    .chars()
                    .map(Character::getNumericValue)
                    .asLongStream()
                    .reduce(1, (x,y) -> x*y);
            if (p > greatest)
                greatest = p;
        }
        return greatest;
    }

    public static void main(String[] args) {
        String number = "73167176531330624919225119674426574742355349194934" +
                        "96983520312774506326239578318016984801869478851843" +
                        "85861560789112949495459501737958331952853208805511" +
                        "12540698747158523863050715693290963295227443043557" +
                        "66896648950445244523161731856403098711121722383113" +
                        "62229893423380308135336276614282806444486645238749" +
                        "30358907296290491560440772390713810515859307960866" +
                        "70172427121883998797908792274921901699720888093776" +
                        "65727333001053367881220235421809751254540594752243" +
                        "52584907711670556013604839586446706324415722155397" +
                        "53697817977846174064955149290862569321978468622482" +
                        "83972241375657056057490261407972968652414535100474" +
                        "82166370484403199890008895243450658541227588666881" +
                        "16427171479924442928230863465674813919123162824586" +
                        "17866458359124566529476545682848912883142607690042" +
                        "24219022671055626321111109370544217506941658960408" +
                        "07198403850962455444362981230987879927244284909188" +
                        "84580156166097919133875499200524063689912560717606" +
                        "05886116467109405077541002256983155200055935729725" +
                        "71636269561882670428252483600823257530420752963450";
        System.out.println("The value of the greatest product of 13 adjacent digits is:");
        System.out.println(greatestProduct(number, 13));
    }

}