703_kth_largest_element_in_a_stream.md

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

import heapq


class KthLargest:

    def __init__(self, k: int, nums: List[int]):
        self.nums = nums
        self.k = k
        heapq.heapify(self.nums)

        while len(self.nums) > k:
            heapq.heappop(self.nums)
        

    def add(self, val: int) -> int:
        if len(self.nums) < self.k:
            heapq.heappush(self.nums, val)
        elif val > self.nums[0]:
            heapq.heapreplace(self.nums, val)
        return self.nums[0]


if __name__ == '__main__':
    l = KthLargest(3, [4, 5, 8, 2])
    print(l.add(3))
    print(l.add(5))
    print(l.add(10))
    print(l.add(9))
    print(l.add(4))