友愛数

AmicableNumberLogic.java

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

import lombok.Builder;
import lombok.Getter;
import lombok.ToString;

public class AmicableNumberLogic {

  public List<AmicableNumbers> process(Integer start, Integer end) {
    return IntStream.rangeClosed(start, end).boxed()
        .map(i -> process(i))
        .filter(amic -> amic != null)
        .peek(System.out :: println)
        .collect(Collectors.toList());
  }

  public AmicableNumbers process(Integer target) {
    Integer primary = divisorSummary(target);
    Integer secondary = divisorSummary(primary);

    if (primary == null || secondary == null) {
      return null;
    }

    if (primary.intValue() <= secondary.intValue()) {
      return null;
    }

    if (target.intValue() == secondary.intValue()) {
      return AmicableNumbers.builder().primary(primary).secondary(secondary).build();
    }

    return null;
  }

  private Integer divisorSummary(Integer target) {
    List<Integer> divisor = Divisor.process(target);
    divisor.remove(divisor.size() -1);
    if (divisor.isEmpty()) {
      return null;
    }

    return divisor.stream().reduce((i1,i2) -> i1+i2).get();
  }

  @Builder @Getter @ToString
  public static class AmicableNumbers {
    private Integer primary;
    private Integer secondary;
  }
}

AmicableNumberLogicTest.groovy

import spock.lang.Specification
import spock.lang.Unroll

@Unroll
class AmicableNumberLogicTest extends Specification {
  AmicableNumberLogic sut = new AmicableNumberLogic()

  def "友愛数_#primary"() {
    when:
    def expect = sut.process(primary)

    then:
    expect.primary == $primary
    expect.secondary == $secondary

    where:
    primary || $primary | $secondary
    220     || 284      | 220
    1184    || 1210     | 1184
    2620    || 2924     | 2620
  }

  def "友愛数一覧"() {
    when:
    def expect = sut.process(2, 10000)

    then:
    expect
    expect.get(0).primary == 284
    expect.get(0).secondary == 220
    expect.get(1).primary == 1210
    expect.get(1).secondary == 1184
    expect.get(2).primary == 2924
    expect.get(2).secondary == 2620
    expect.get(3).primary == 5564
    expect.get(3).secondary == 5020
    expect.get(4).primary == 6368
    expect.get(4).secondary == 6232

  }
}