FibonacciJavaStreams.java

packagecom.thealgorithms.maths;

importjava.math.BigDecimal;
importjava.util.List;
importjava.util.Optional;
importjava.util.stream.Stream;

/**
 * @author: caos321
 * @date: 14 October 2021 (Thursday)
 */
publicfinalclassFibonacciJavaStreams {
privateFibonacciJavaStreams() {
 }

publicstaticOptional<BigDecimal> calculate(finalBigDecimalindex) {
if (index == null || index.compareTo(BigDecimal.ZERO) < 0) {
thrownewIllegalArgumentException("Input index cannot be null or negative!");
 }

if (index.compareTo(BigDecimal.ONE) < 0) {
returnOptional.of(BigDecimal.ZERO);
 }

if (index.compareTo(BigDecimal.TWO) < 0) {
returnOptional.of(BigDecimal.ONE);
 }

finalList<BigDecimal> results = Stream.iterate(index, x -> x.compareTo(BigDecimal.ZERO) > 0, x -> x.subtract(BigDecimal.ONE))
 .reduce(List.of(), (list, current) -> list.isEmpty() || list.size() < 2 ? List.of(BigDecimal.ZERO, BigDecimal.ONE) : List.of(list.get(1), list.get(0).add(list.get(1))), (list1, list2) -> list1);

returnresults.isEmpty() ? Optional.empty() : Optional.of(results.get(results.size() - 1));
 }
}