703 Kth Largest Element in a Stream

703. Kth Largest Element in a Stream

1. Question

Design a class to find thekth 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 integerkand an integer arraynums, which contains initial elements from the stream. For each call to the methodKthLargest.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 andk≥ 1.

2. Implementation

思路： 用Heap解决数据流第K大的问题

class KthLargest {
    PriorityQueue<Integer> minHeap;
    int size;

    public KthLargest(int k, int[] nums) {
        minHeap = new PriorityQueue<Integer>(k);
        size = k;

        for (int num : nums) {
            add(num);
        }
    }

    public int add(int val) {
        if (minHeap.size() < size) {
            minHeap.add(val);
        }
        else if (minHeap.peek() < val) {
            minHeap.remove();
            minHeap.add(val);
        }
        return minHeap.peek();
    }
}

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

3. Time & Space Complexity

Heap: 时间复杂度O(nlogk), 空间复杂度O(k)