找出数组的第 K 大和

/*
 * 思路：
 * 1. 计算所有可能的子序列和，并将其存储在一个集合中。
 * 2. 使用Java Stream对这些子序列和进行排序，然后获取第 k 大的和。
 */
import java.util.*;
import java.util.stream.Collectors;

public class KthLargestSubsequenceSumStream {
    public int getKthLargestSum(int[] nums, int k) {
        Set<Integer> subsequenceSums = new HashSet<>();
        generateSubsequenceSums(nums, 0, 0, subsequenceSums);
        List<Integer> sortedSums = subsequenceSums.stream()
            .sorted(Comparator.reverseOrder())
            .collect(Collectors.toList());
        return sortedSums.get(k - 1);
    }

    private void generateSubsequenceSums(int[] nums, int index, int currentSum, Set<Integer> subsequenceSums) {
        if (index == nums.length) {
            subsequenceSums.add(currentSum);
            return;
        }
        generateSubsequenceSums(nums, index + 1, currentSum + nums[index], subsequenceSums);
        generateSubsequenceSums(nums, index + 1, currentSum, subsequenceSums);
    }

    public static void main(String[] args) {
        KthLargestSubsequenceSumStream solver = new KthLargestSubsequenceSumStream();
        int[] nums = {2, 4, -2};
        int k = 5;
        System.out.println(solver.getKthLargestSum(nums, k));  // 输出: 2
    }
}