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703. Kth Largest Element in a 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:

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

Solution:

class KthLargest {
    PriorityQueue<Integer> minHeap = new PriorityQueue<Integer>();
    int k;

    public KthLargest(int k, int[] nums) {
        this.k = k;
        for (int i = 0; i < nums.length; i++){ // O(n)
            add(nums[i]);
        } 
    }

    public int add(int val) { // O(logn)
        minHeap.offer(val);
        if (minHeap.size() > k){
            minHeap.poll();
        }

        return minHeap.peek();  

    }
}

// TC: O(nlogn)
// SC: O(n)

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