703. Kth Largest Element in a Stream

问题
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.

优先级队列，插入所有元素，小元素在前。
当队列长度大于k时，poll掉前面的元素。

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