LeetCode-in-Java

703. Kth Largest Element in a Stream

Easy

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:

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.

Solution

import java.util.PriorityQueue;

public class KthLargest {
    private final int maxSize;
    private final PriorityQueue<Integer> heap;

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

    public int add(int val) {
        if (heap.size() < maxSize) {
            heap.add(val);
        } else if (heap.peek() < val) {
            heap.add(val);
            heap.poll();
        }
        return heap.peek();
    }
}

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