/* __ __ __ __ __ ___
* \ \ / / \ \ / / __/
* \ \/ / /\ \ \/ / /
* \____/__/ \__\____/__/.ɪᴏ
* ᶜᵒᵖʸʳᶦᵍʰᵗ ᵇʸ ᵛᵃᵛʳ ⁻ ˡᶦᶜᵉⁿˢᵉᵈ ᵘⁿᵈᵉʳ ᵗʰᵉ ᵃᵖᵃᶜʰᵉ ˡᶦᶜᵉⁿˢᵉ ᵛᵉʳˢᶦᵒⁿ ᵗʷᵒ ᵈᵒᵗ ᶻᵉʳᵒ
*/
package io.vavr.collection.euler;
import io.vavr.collection.Stream;
import org.junit.Test;
import static org.assertj.core.api.Assertions.assertThat;
public class Euler48Test {
private static final long MOD = 10_000_000_000L;
/**
* <strong>Problem 48: Self powers</strong>
* <p>
* The series, 1<sup>1</sup> + 2<sup>2</sup> + 3<sup>3</sup> + ... + 10<sup>10</sup> = 10405071317.
* <p>
* Find the last ten digits of the series, 1<sup>1</sup> + 2<sup>2</sup> + 3<sup>3</sup> + ... + 1000<sup>1000</sup>.
* <p>
* See also <a href="https://projecteuler.net/problem=48">projecteuler.net problem 48</a>.
*/
@Test
public void shouldSolveProblem48() {
assertThat(sumPowers(10)).isEqualTo(405_071_317L);
assertThat(sumPowers(1000)).isEqualTo(9_110_846_700L);
}
private static long sumPowers(int max) {
return Stream.range(1, max)
.map(Euler48Test::selfPower)
.reduce(Euler48Test::sumMod);
}
private static long selfPower(long v) {
final Stream<Long> powers = Stream.iterate(v, el -> multMod(el, el));
return bits(v)
.map(powers::get)
.prepend(1L)
.reduce(Euler48Test::multMod);
}
private static long multMod(long v1, long v2) {
final Stream<Long> shifts = Stream.iterate(v1, el -> sumMod(el, el));
return bits(v2)
.map(shifts::get)
.prepend(0L)
.reduce(Euler48Test::sumMod);
}
private static long sumMod(long v1, long v2) {
return (v1 + v2) % MOD;
}
private static Stream<Integer> bits(long v) {
return Stream.from(0)
.takeWhile(b -> (v >> b) > 0)
.filter(b -> ((v >> b) & 1) != 0);
}
}