LeetCode 703. Kth Largest Element in a Stream

Posted 2021-01-12 Dylan_Java_NYC

原题链接在这里：https://leetcode.com/problems/kth-largest-element-in-a-stream/description/

题目：

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.

题解：

用minHeap维持size在k. 

Time Complexity: KthLargest, O(n * logk). add O(logk). n = nums.length. 

Space: O(k).

AC Java:

 1 class KthLargest {
 2     PriorityQueue<Integer> minHeap;
 3     int k;
 4     
 5     public KthLargest(int k, int[] nums) {
 6         this.minHeap = new PriorityQueue<Integer>();
 7         this.k = k;
 8         for(int num : nums){
 9             add(num);
10         }
11     }
12     
13     public int add(int val) {
14         if(minHeap.size() < k){
15             minHeap.add(val);
16         }else if(minHeap.peek() < val){
17             minHeap.poll();
18             minHeap.add(val);
19         }
20         
21         return minHeap.peek();
22     }
23 }
24 
25 /**
26  * Your KthLargest object will be instantiated and called as such:
27  * KthLargest obj = new KthLargest(k, nums);
28  * int param_1 = obj.add(val);
29  */