703. Kth Largest Element in a Stream

Tags: Easy Heap

Links: https://leetcode.com/problems/kth-largest-element-in-a-stream/

---

Design a class to find the **k**th 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.

---

class KthLargest {
    priority_queue<int, vector<int>, greater<int>> pq;
    int kth;
public:
    KthLargest(int k, vector<int>& nums) {
        for (auto e : nums) {
            pq.push(e);
        }
        while (pq.size() > k) {
            pq.pop();
        }
        kth = k;
    }

    int add(int val) {
        if (pq.size() < kth) pq.push(val);
        else if (val > pq.top()) {
            pq.pop(); pq.push(val);
        }
        return pq.top();
    }
};

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