循环遍历ArrayList的所有可能组合

import java.util.ArrayList;
import java.util.List;

public class ArrayListCombination {
    public static void main(String[] args) {
        List<Integer> nums = new ArrayList<>();
        nums.add(1);
        nums.add(2);
        nums.add(3);

        List<List<Integer>> result = new ArrayList<>();
        backtrack(nums, new ArrayList<>(), result, 0);

        for (List<Integer> combination : result) {
            System.out.println(combination);
        }
    }

    private static void backtrack(List<Integer> nums, List<Integer> temp, List<List<Integer>> result, int start) {
        result.add(new ArrayList<>(temp));

        for (int i = start; i < nums.size(); i++) {
            temp.add(nums.get(i));
            backtrack(nums, temp, result, i + 1);
            temp.remove(temp.size() - 1);
        }
    }
}

[]
[1]
[1, 2]
[1, 2, 3]
[1, 3]
[2]
[2, 3]
[3]