自写最小堆模板类

template<class T>
struct Priority_queue{
    T *a;
    void init(){
        num = 0;
    }
    Priority_queue(int n=1100000){
        a = new T[n];
        num = 0;
    }
    int num;
    int size(){
        return num;
    }
    void push(const T &x){
        num+=1;
        a[num] = x;
        int k = num;
        while(k>1){
            int p = k/2;
            if(a[k]<a[p]){
                T temp = a[k];
                a[k] = a[p];
                a[p] = temp;
                k = p;
            }
            else
                break;
        }
    }
    bool empty(){
        if(num<=0)
            return 1;
        else 
            return 0;
    }
    T top(){
        return a[1];
    }
    T pop(){
        T key = a[1];
        a[1] = a[num];
        num -=1;
        int pt = 1;
        while(pt<=num){
             int pr;
            if(a[pt*2+1]<a[pt*2]){
                pr = pt*2+1;
            }
            else
                pr = pt*2;
            if(a[pr]<a[pt]){
                T temp = a[pr];
                a[pr] = a[pt];
                a[pt] = temp;
                pt = pr;
            }
            else
                break;
        }
        return key;
    }
};