[LeetCode] 703. Kth Largest Element in a Stream - 문제풀이

Description

스트림에 정렬된 순서에서 가장 큰 요소를 찾는 클래스를 디자인 합니다.

Design a class to find the kth largest element in a stream. Note that it is the kth largest element in the sorted order, not the kth distinct element.

Implement KthLargest class:

• KthLargest(int k, int[] nums) Initializes the object with the integer k and the stream of integers nums.
• int add(int val) Appends the integer val to the stream and returns the element representing the kth largest element in the stream.

Example 1:

Input
["KthLargest", "add", "add", "add", "add", "add"]
[[3, [4, 5, 8, 2]], [3], [5], [10], [9], [4]]
Output
[null, 4, 5, 5, 8, 8]

Explanation
KthLargest kthLargest = new KthLargest(3, [4, 5, 8, 2]);
kthLargest.add(3);   // return 4
kthLargest.add(5);   // return 5
kthLargest.add(10);  // return 5
kthLargest.add(9);   // return 8
kthLargest.add(4);   // return 8

Constraints:

• 1 <= k <= 104
• 0 <= nums.length <= 104
• -10^4 <= nums[i] <= 10^4
• -10^4 <= val <= 10^4
• At most 10^4 calls will be made to add.
• It is guaranteed that there will be at least k elements in the array when you search for the kth element.

Solution 1. PriorityQueue

public class KthLargest {

    private final PriorityQueue<Integer> q;
    private final int k;

    public KthLargest(int k, int[] nums) {
        this.k = k;
        q = new PriorityQueue<Integer>(k);
        for (int a :nums) {
            add(a);
        }
    }

    public int add(int val) {
        q.offer(val);
        if (q.size() > k) {
            q.poll();
        }
        return q.peek();
    }
}

우선순위 큐를 이용하여 k사이즈보다 큰 값은 poll해가며 우선순위를 유지한뒤 가장 큰값을 peek 해줍니다.

Reference

Kth Largest Element in a Stream - LeetCode