703. Kth Largest Element in a Stream*

703. Kth Largest Element in a Stream*

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

Title Description

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.

C ++ implementation 1

Minimum heap, to save the maximum number of k, wherein k-th top of the stack is the maximum number.

class KthLargest {
public:
    int size = 0;
    // 使用最小堆, 保证堆顶为第 k 个最大的数.
    priority_queue<int, vector<int>, std::greater<int>> q;
    KthLargest(int k, vector<int>& nums) {
        for (int i = 0; i < nums.size(); ++ i) {
            q.push(nums[i]);
            if (q.size() > k) q.pop();
        }
        size = k;
    }
    
    int add(int val) {
        q.push(val);
        if (q.size() > size) q.pop();
        return q.top();
    }
};