README.md

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.

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.

Solutions (Rust)

1. Sort

struct KthLargest {
    k: usize,
    elements: Vec<i32>,
}


/** 
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl KthLargest {

    fn new(k: i32, nums: Vec<i32>) -> Self {
        Self {
            k: k as usize,
            elements: nums,
        }
    }

    fn add(&mut self, val: i32) -> i32 {
        self.elements.push(val);
        self.elements.sort_unstable_by(|a, b| b.cmp(a));
        self.elements[self.k - 1]
    }
}

/**
 * Your KthLargest object will be instantiated and called as such:
 * let obj = KthLargest::new(k, nums);
 * let ret_1: i32 = obj.add(val);
 */

2. Min Heap

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

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


/** 
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl KthLargest {

    fn new(k: i32, nums: Vec<i32>) -> Self {
        let mut kth_largest = Self {
            k: k as usize,
            elements: BinaryHeap::with_capacity(k as usize),
        };

        for num in nums {
            kth_largest.add(num);
        }

        kth_largest
    }

    fn add(&mut self, val: i32) -> i32 {
        if self.elements.len() < self.k {
            self.elements.push(Reverse(val));
        } else if self.elements.peek() > Some(&Reverse(val)) {
            self.elements.pop();
            self.elements.push(Reverse(val));
        }

        match self.elements.peek() {
            Some(&Reverse(x)) => x,
            None => 0,
        }
    }
}

/**
 * Your KthLargest object will be instantiated and called as such:
 * let obj = KthLargest::new(k, nums);
 * let ret_1: i32 = obj.add(val);
 */