LeetCode - Kth Largest Element in a Stream

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.

Your KthLargest class will have a constructor which accepts an integer k and an integer array nums, which contains initial elements from the stream. For each call to the method KthLargest.add, return the element representing the kth largest element in the stream.

Example:

int k = 3;
int[] arr = [4,5,8,2];
KthLargest kthLargest = new KthLargest(3, arr);
kthLargest.add(3);   // returns 4
kthLargest.add(5);   // returns 5
kthLargest.add(10);  // returns 5
kthLargest.add(9);   // returns 8
kthLargest.add(4);   // returns 8
Note:
You may assume that nums' length ≥ k-1 and k ≥ 1.

遍历数组时将数字加入优先队列（堆），一旦堆的大小大于k就将堆顶元素去除，确保堆的大小为k。遍历完后堆顶就是返回值。

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

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

/**
 * Your KthLargest object will be instantiated and called as such:
 * KthLargest obj = new KthLargest(k, nums);
 * int param_1 = obj.add(val);
 */