703. Kth Largest Element in a Stream

Description

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

 

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.

 

Solutions

Solution: Binary Search

• Time complexity: O(nlogk)
• Space complexity: O(k)

 

JavaScript

/**
 * @param {number} k
 * @param {number[]} nums
 */
const KthLargest = function (k, nums) {
  this.k = k;
  this.nums = nums.sort((a, b) => a - b).slice(-k);
};

/**
 * @param {number} val
 * @return {number}
 */
KthLargest.prototype.add = function (val) {
  let left = 0;
  let right = this.nums.length;

  while (left < right) {
    const mid = Math.floor((left + right) / 2);

    this.nums[mid] >= val ? (right = mid) : (left = mid + 1);
  }
  this.nums.splice(left, 0, val);

  if (this.nums.length > this.k) {
    this.nums.shift();
  }
  return this.nums[0];
};

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