第 k 个数

/*
 * 题目思路:
 * 使用Java Stream API同样需要实现最小堆和去重机制。
 * 由于Stream不直接支持优先队列，我们仍然需要结合使用PriorityQueue和HashSet。
 */
import java.util.HashSet;
import java.util.PriorityQueue;
import java.util.stream.Stream;

public class KthNumberWithPrimeFactorsStream {
    public int getKthMagicNumber(int k) {
        if (k <= 0) return 0;
        PriorityQueue<Long> minHeap = new PriorityQueue<>();
        HashSet<Long> seen = new HashSet<>();
        long[] primes = {3, 5, 7};
        minHeap.add(1L);
        seen.add(1L);
        long number = 1;
        for (int i = 0; i < k; i++) {
            number = minHeap.poll();
            for (long prime : primes) {
                long newNumber = number * prime;
                if (!seen.contains(newNumber)) {
                    seen.add(newNumber);
                    minHeap.add(newNumber);
                }
            }
        }
        return (int) number;
    }
    public static void main(String[] args) {
        KthNumberWithPrimeFactorsStream solution = new KthNumberWithPrimeFactorsStream();
        System.out.println(solution.getKthMagicNumber(5)); // 输出: 9
    }
}