LeetCode 2802: Find The K-th Lucky Number Solution
Master LeetCode problem 2802 (Find The K-th Lucky Number), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.
2802. Find The K-th Lucky Number
Problem Explanation
Explanation:
To solve this problem, we can use a priority queue (min-heap) to find the k-th lucky number. We start with the number 1 in the priority queue, then repeatedly extract the minimum number from the queue, and for each extracted number x, we insert both x2 and x3 into the queue. We continue this process until we have extracted k numbers from the queue, at which point we return the k-th number as the answer.
The idea behind this approach is that by generating new lucky numbers from the current lucky numbers (either by multiplying by 2 or 3), we ensure that the numbers in the priority queue are always in sorted order. This allows us to efficiently find the k-th lucky number by extracting k times from the priority queue.
Time Complexity:
The time complexity of this approach is O(k*log(k)) where k is the input parameter denoting the k-th lucky number to find.
Space Complexity:
The space complexity of this approach is O(k) to store the k lucky numbers in the priority queue.
:
Solution Code
import java.util.PriorityQueue;
class Solution {
public int findKthLucky(int k) {
PriorityQueue<Long> pq = new PriorityQueue<>();
pq.offer(1L);
for (int i = 0; i < k - 1; i++) {
long current = pq.poll();
pq.offer(current * 2);
pq.offer(current * 3);
}
return Math.toIntExact(pq.poll());
}
}Try It Yourself
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