priority_queue 排序

两种写法等价（都是按照 堆顶是 x小的）但是在did内直接重载快得多！！！

struct did{
	int x,y;
	bool operator<(const did& t)const{
		return t.x<x;
	}
};
struct cmp{
	bool operator()(did &a,did &b)
	{
		return a.x>b.x;
	}
};
priority_queue<did>q;

priority_queue<did,vector<did> ,cmp>q;