剑指offer

手写最大堆-实现

class Heap {
    public:
    void push(int x){
        heap.push_back(x);
        size += 1;
        int now = size;
        while(now!=1) {
            int parent = now / 2;
            if(heap[now] > heap[parent])
                swap(heap[now], heap[parent]);
            else break;
            now = parent;
        }
    }
    
    bool empty(){
        return size == 0;
    }
    
    int top(){
       return heap[1];
    }
    
    int _size(){
        return size;
    }
    
    int pop(){
        int ans = heap[1];
        swap(heap[size], heap[1]);
        heap.pop_back();
        size -= 1;
        int now = 1;
        while(now * 2 <= size){
            int child = now * 2;
            if(child + 1 <=size && heap[child+1] > heap[child])
                child += 1;
            if(heap[now] < heap[child])
                swap(heap[now], heap[child]);
            else break;
            now = child;
        }
        return ans;
    }
    
    private:
    vector<int> heap = {0};
    int size = 0;
};


class Solution {
public:
    vector<int> GetLeastNumbers_Solution(vector<int> input, int k) {
        Heap h;
        vector<int> ans;
        if(k>input.size()) return ans;
        for(auto it: input) {
            if(h._size()<k)
                h.push(it);
            else{
                if(h.top()>it) {
                    h.pop();
                    h.push(it);
                }
            }
        }
        while(!h.empty()) ans.push_back(h.pop());
        reverse(ans.begin(), ans.end());
        return ans;
    }
};