Euler99Test.java

/*                        __    __  __  __    __  ___
 *                       \  \  /  /    \  \  /  /  __/
 *                        \  \/  /  /\  \  \/  /  /
 *                         \____/__/  \__\____/__/.ɪᴏ
 * ᶜᵒᵖʸʳᶦᵍʰᵗ ᵇʸ ᵛᵃᵛʳ ⁻ ˡᶦᶜᵉⁿˢᵉᵈ ᵘⁿᵈᵉʳ ᵗʰᵉ ᵃᵖᵃᶜʰᵉ ˡᶦᶜᵉⁿˢᵉ ᵛᵉʳˢᶦᵒⁿ ᵗʷᵒ ᵈᵒᵗ ᶻᵉʳᵒ
 */
package io.vavr.collection.euler;

import org.junit.Test;

import static java.util.Arrays.asList;
import static io.vavr.collection.euler.Utils.file;
import static io.vavr.collection.euler.Utils.readLines;
import static org.assertj.core.api.Assertions.assertThat;

public class Euler99Test {

    /**
     * <strong>Problem 99: Largest exponential</strong>
     * <p>
     * Comparing two numbers written in index form like 2<sup>11</sup> and 3<sup>7</sup> is not difficult,
     * as any calculator would confirm that 2<sup>11</sup> = 2048 < 3<sup>7</sup> = 2187.
     * <p>
     * However, confirming that 632382<sup>518061</sup> > 519432<sup>525806</sup> would be much more difficult,
     * as both numbers contain over three million digits.
     * <p>
     * Using p099_base_exp.txt, a 22K text file containing one thousand lines with a base/exponent pair on each line,
     * determine which line number has the greatest numerical value.
     * <p>
     * See also <a href="https://projecteuler.net/problem=99">projecteuler.net problem 99</a>.
     */
    @Test
    public void shouldSolveProblem99() {
        assertThat(solve()).isEqualTo(709);
    }

    private static long solve() {
        return readLines(file("p099_base_exp.txt"))
                .flatMap(s -> asList(s.split(",")))
                .map(Integer::parseInt)
                .grouped(2)
                .map(t -> t.get(1) * Math.log(t.get(0)))
                .zipWithIndex()
                .reduce((t1, t2) -> t1._1 > t2._1 ? t1 : t2)
                ._2 + 1;
    }
}