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) 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.

Rust Solution

use std::cmp::Reverse;
use std::collections::BinaryHeap;

struct KthLargest {
    pq: BinaryHeap<Reverse<i32>>,
    k: usize,
}

impl KthLargest {
    fn new(k: i32, nums: Vec<i32>) -> Self {
        let mut pq: BinaryHeap<Reverse<i32>> = BinaryHeap::new();
        let k = k as usize;
        for x in nums {
            pq.push(Reverse(x));
            if pq.len() > k {
                pq.pop();
            }
        }
        KthLargest { pq, k }
    }

    fn add(&mut self, val: i32) -> i32 {
        self.pq.push(Reverse(val));
        if self.pq.len() > self.k {
            self.pq.pop();
        }
        let x = *self.pq.peek().unwrap();
        x.0
    }
}

#[test]
fn test() {
    let k = 3;
    let nums = vec![4, 5, 8, 2];
    let mut obj = KthLargest::new(k, nums);
    assert_eq!(obj.add(3), 4);
    assert_eq!(obj.add(5), 5);
    assert_eq!(obj.add(10), 5);
    assert_eq!(obj.add(9), 8);
    assert_eq!(obj.add(4), 8);
}

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