# 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
[[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]);


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

• class KthLargest {
private PriorityQueue<Integer> q;
private int size;

public KthLargest(int k, int[] nums) {
q = new PriorityQueue<>(k);
size = k;
for (int num : nums) {
}
}

q.offer(val);
if (q.size() > size) {
q.poll();
}
return q.peek();
}
}

/**
* Your KthLargest object will be instantiated and called as such:
* KthLargest obj = new KthLargest(k, nums);
*/

• class KthLargest {
public:
priority_queue<int, vector<int>, greater<int>> q;
int size;

KthLargest(int k, vector<int>& nums) {
size = k;
for (int num : nums) add(num);
}

q.push(val);
if (q.size() > size) q.pop();
return q.top();
}
};

/**
* Your KthLargest object will be instantiated and called as such:
* KthLargest* obj = new KthLargest(k, nums);
*/

• class KthLargest:
def __init__(self, k: int, nums: List[int]):
self.q = []
self.size = k
for num in nums:

def add(self, val: int) -> int:
heappush(self.q, val)
if len(self.q) > self.size:
heappop(self.q)
return self.q[0]

# Your KthLargest object will be instantiated and called as such:
# obj = KthLargest(k, nums)


• type KthLargest struct {
h *IntHeap
k int
}

func Constructor(k int, nums []int) KthLargest {
h := &IntHeap{}
heap.Init(h)
for _, v := range nums {
heap.Push(h, v)
}

for h.Len() > k {
heap.Pop(h)
}

return KthLargest{
h: h,
k: k,
}
}

func (this *KthLargest) Add(val int) int {
heap.Push(this.h, val)
for this.h.Len() > this.k {
heap.Pop(this.h)
}

return this.h.Top()
}

func connectSticks(sticks []int) int {
h := IntHeap(sticks)
heap.Init(&h)
res := 0
for h.Len() > 1 {
val := heap.Pop(&h).(int)
val += heap.Pop(&h).(int)
res += val
heap.Push(&h, val)
}
return res
}

type IntHeap []int

func (h IntHeap) Len() int           { return len(h) }
func (h IntHeap) Less(i, j int) bool { return h[i] < h[j] }
func (h IntHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
func (h *IntHeap) Push(x any) {
*h = append(*h, x.(int))
}
func (h *IntHeap) Pop() any {
old := *h
n := len(old)
x := old[n-1]
*h = old[0 : n-1]
return x
}

func (h *IntHeap) Top() int {
if (*h).Len() == 0 {
return 0
}

return (*h)[0]
}

/**
* Your KthLargest object will be instantiated and called as such:
* obj := Constructor(k, nums);
*/

• /**
* @param {number} k
* @param {number[]} nums
*/
var KthLargest = function (k, nums) {
this.k = k;
this.heap = new MinHeap();
for (let num of nums) {
}
};

/**
* @param {number} val
* @return {number}
*/
this.heap.offer(val);
if (this.heap.size() > this.k) {
this.heap.poll();
}
return this.heap.peek();
};

class MinHeap {
constructor(data = []) {
this.data = data;
this.comparator = (a, b) => a - b;
this.heapify();
}

heapify() {
if (this.size() < 2) return;
for (let i = 1; i < this.size(); i++) {
this.bubbleUp(i);
}
}

peek() {
if (this.size() === 0) return null;
return this.data[0];
}

offer(value) {
this.data.push(value);
this.bubbleUp(this.size() - 1);
}

poll() {
if (this.size() === 0) {
return null;
}
const result = this.data[0];
const last = this.data.pop();
if (this.size() !== 0) {
this.data[0] = last;
this.bubbleDown(0);
}
return result;
}

bubbleUp(index) {
while (index > 0) {
const parentIndex = (index - 1) >> 1;
if (this.comparator(this.data[index], this.data[parentIndex]) < 0) {
this.swap(index, parentIndex);
index = parentIndex;
} else {
break;
}
}
}

bubbleDown(index) {
const lastIndex = this.size() - 1;
while (true) {
const leftIndex = index * 2 + 1;
const rightIndex = index * 2 + 2;
let findIndex = index;
if (
leftIndex <= lastIndex &&
this.comparator(this.data[leftIndex], this.data[findIndex]) < 0
) {
findIndex = leftIndex;
}
if (
rightIndex <= lastIndex &&
this.comparator(this.data[rightIndex], this.data[findIndex]) < 0
) {
findIndex = rightIndex;
}
if (index !== findIndex) {
this.swap(index, findIndex);
index = findIndex;
} else {
break;
}
}
}

swap(index1, index2) {
[this.data[index1], this.data[index2]] = [this.data[index2], this.data[index1]];
}

size() {
return this.data.length;
}
}

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