703. Kth Largest Element in a Stream

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703. Kth Largest Element in a Stream

Description

Difficulty: Easy

Related Topics: Tree, Design, Binary Search Tree, Heap (Priority Queue), Binary Tree, Data 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.

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:

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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
  • -104 <= nums[i] <= 104
  • -104 <= val <= 104
  • At most 104 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.

Hints/Notes

  • 2023/10/17
  • priority queue
  • No solution from 0x3F

Solution

Language: C++

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class KthLargest {
public:
    priority_queue<int, vector<int>, greater<int>> pq;
    int size;

    KthLargest(int k, vector<int>& nums) {
        size = k;
        for (int num : nums) {
            addItem(num);
        }
    }

    void addItem(int val) {
        pq.push(val);
        if (pq.size() > size) {
            pq.pop();
        }
    }
    
    int add(int val) {
        addItem(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);
 */