因子的组合

import java.util.*;
import java.util.stream.*;
 
public class Solution {
    /**
     * This method finds all factor combinations of a given number using Java Streams.
     * 
     * @param n the target number
     * @return a list of lists containing factor combinations
     */
    public List<List<Integer>> getFactors(int n) {
        return IntStream.rangeClosed(2, n)
                        .filter(i -> n % i == 0)
                        .boxed()
                        .flatMap(i -> getFactors(n / i).stream()
                        .filter(list -> list.isEmpty() || i <= list.get(0))
                        .map(list -> {
                            List<Integer> newList = new ArrayList<>(list);
                            newList.add(0, i);
                            return newList;
                        }))
                        .collect(Collectors.toList());
    }
 
    /**
     * Overloaded method to include a default start factor.
     * 
     * @param n the target number
     * @param start the starting factor
     * @return a list of lists containing factor combinations
     */
    private List<List<Integer>> getFactors(int n, int start) {
        if (n <= 1) return Arrays.asList(Collections.emptyList());
        return IntStream.rangeClosed(start, n)
                        .filter(i -> n % i == 0)
                        .boxed()
                        .flatMap(i -> getFactors(n / i, i).stream()
                        .filter(list -> list.isEmpty() || i <= list.get(0))
                        .map(list -> {
                            List<Integer> newList = new ArrayList<>(list);
                            newList.add(0, i);
                            return newList;
                        }))
                        .collect(Collectors.toList());
    }
}