c++优先队列小节（常常弄混）

常见四种形式:

1. priority_queue p1;
2. priority_queue p2;
3. priority_queue,greater > p3;
4. priority_queue,less > p4;

1. priority_queue p1;

大根堆：从大到小排序

	priority_queue p1;
	p1.push(1);
	p1.push(2);
	p1.push(5);
	p1.push(3); 
	
	while(!p1.empty()){
		int t = p1.top();
		p1.pop();
		
		cout << t << endl;
	}
	cout << "=================" << endl; 

2. priority_queue p2;

大根堆：按照first从大到小排序

	priority_queue p2; 
	p2.push(mp(1,2));
	p2.push(mp(2,4));
	p2.push(mp(3,1));
	p2.push(mp(4,2));
	p2.push(mp(5,4));
	p2.push(mp(6,1));
	
	while(!p2.empty()){
		PII t = p2.top();
		p2.pop();
		
		cout << t.fi << " " << t.se << endl;
	}
	cout << "=================" << endl; 

3. priority_queue,greater > p3;

小根堆：按照first从小到大排序

	priority_queue,greater > p3; 
	p3.push(mp(1,2));
	p3.push(mp(2,4));
	p3.push(mp(3,1));
	p3.push(mp(4,2));
	p3.push(mp(5,4));
	p3.push(mp(6,1));
	
	while(!p3.empty()){
		PII t = p3.top();
		p3.pop();
		
		cout << t.fi << " " << t.se << endl;
	}
	cout << "=================" << endl; 	

4. priority_queue,less > p4;

大根堆：跟默认一样

	priority_queue,less > p4; 
	p4.push(mp(1,2));
	p4.push(mp(2,4));
	p4.push(mp(3,1));
	p4.push(mp(4,2));
	p4.push(mp(5,4));
	p4.push(mp(6,1));
	
	while(!p4.empty()){
		PII t = p4.top();
		p4.pop();
		
		cout << t.fi << " " << t.se << endl;
	}
	cout << "=================" << endl;