Euler 8

Solution.java

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class Solution {

    static String rawString = "73167176531330624919225119674426574742355349194934\n" +
            "96983520312774506326239578318016984801869478851843\n" +
            "85861560789112949495459501737958331952853208805511\n" +
            "12540698747158523863050715693290963295227443043557\n" +
            "66896648950445244523161731856403098711121722383113\n" +
            "62229893423380308135336276614282806444486645238749\n" +
            "30358907296290491560440772390713810515859307960866\n" +
            "70172427121883998797908792274921901699720888093776\n" +
            "65727333001053367881220235421809751254540594752243\n" +
            "52584907711670556013604839586446706324415722155397\n" +
            "53697817977846174064955149290862569321978468622482\n" +
            "83972241375657056057490261407972968652414535100474\n" +
            "82166370484403199890008895243450658541227588666881\n" +
            "16427171479924442928230863465674813919123162824586\n" +
            "17866458359124566529476545682848912883142607690042\n" +
            "24219022671055626321111109370544217506941658960408\n" +
            "07198403850962455444362981230987879927244284909188\n" +
            "84580156166097919133875499200524063689912560717606\n" +
            "05886116467109405077541002256983155200055935729725\n" +
            "71636269561882670428252483600823257530420752963450";

    public static void main(String[] args) {
        List<Long> digits = rawString
            .replace("\n", "")
            .chars()
            .mapToObj(c -> Long.valueOf(c - '0'))
            .collect(Collectors.toList());
        OptionalLong maxProduct = IntStream
            .range(0, digits.size() - 13)
            .mapToLong(idx -> digits.subList(idx, idx + 13).stream().reduce(1L, (num, acc) -> num * acc))
            .max();
        System.out.println(maxProduct.getAsLong());
    }
}