703. Kth Largest Element in a Stream

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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:

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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.

解法1

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class KthLargest {
public:
    KthLargest(int k, vector<int>& nums): vec(nums),kth(k) {
        sort(vec.begin(), vec.end());
    }
    
    int add(int val) {
        int i = vec.size()-1;
        vec.push_back(0);
        while(i>=0 && vec[i]> val){
            vec[i+1] = vec[i];
            --i;
        }
        vec[i+1] = val;
        if(vec.size() < kth){
            throw "no solution";
        }
        return vec[vec.size()-kth];
    }
private:
   vector<int> vec;
    int kth;
};

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

解法2

能不能简化呢？

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class KthLargest {
public:
    KthLargest(int k, vector<int>& nums):kth(k) {
        if(kth == 0){
            return;
        }
        int size = kth > nums.size() ? nums.size() : kth;
        for(int i=0;i<size;++i){
            heap.push_back(nums[i]);
        }
        if(heap.empty()){
            return;
        }
        bulid_tree(heap);
        for(int i=size;i<nums.size();++i){
            if(nums[i] > heap[0]){
                heap[0] = nums[i];
                min_heapify(0, heap);
            }
        }
    }

    int add(int val) {
        if(heap.size() < kth){
            heap.push_back(val);
            min_heapify(0, heap);
        }
        else  if(val > heap[0]){
            heap[0] = val;
            min_heapify(0, heap);
        }
        return heap[0];
    }
    static void min_heapify(int k, vector<int>& nums){
        int key = nums[k];
        bool heap = false;
        while(!heap && 2 * k + 1 < nums.size()){
            int j = 2 * k + 1;
            if(j + 1 < nums.size()){
                if(nums[j + 1] < nums[j]){
                    j = j + 1;
                }
            }
            if(nums[j] >= key){
                heap = true;
            }else{
                nums[k] = nums[j];
                k = j;
            }
        }
        nums[k] = key;
    }
    static void bulid_tree(vector<int>& nums){
        for(int i=nums.size()/2;i>=0;--i){
            min_heapify(i, nums);
        }
    }
    
private:
    vector<int> heap;
    int kth;
};

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