[Go] LeetCode 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.

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.

Solution

package _703_kth_largest_element_in_a_stream

/*  Heap, PriorityQueue */

import (
   "container/heap"
)

// KthLargest object will be instantiated and called as such:
// obj := Constructor(k, nums);
// param_1 := obj.Add(val);
type KthLargest struct {
   k    int
   heap intHeap
}


func Constructor(k int, nums []int) KthLargest {
   h := intHeap(nums)
   //Convert to heap
   heap.Init(&h)

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

func (kl *KthLargest) Add(val int) int {
   heap.Push(&kl.heap, val)

   //Pop minimum element until len(h) = k and kthlargest = h[0]
   for len(kl.heap) > kl.k {
      heap.Pop(&kl.heap)
   }

   return kl.heap[0]
}

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 interface{}) {
   *h = append(*h, x.(int))
}

func (h *intHeap) Pop() interface{} {
   res := (*h)[len(*h)-1]
   *h = (*h)[:len(*h)-1]
   return res
}