Published by
May 5, 2012 (last update: Mar 11, 2013)

priority_queue

Score: 3.3/5 (23 votes)
*****
look at this first :
http://www.cplusplus.com/reference/stl/priority_queue/

now we want to define a priority queue that enable us to Add element to priority queue with custom KEY.


Define Priority Queue



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#include<vector>
using namespace std;
template <class T=int> 
class PriorityQueue
{
private:
	vector<int> Key;
	vector<T> element;
	vector<int>::iterator it;

	
	void insert(const T &value,const int &key ,const int l ,const int h)
	{
		if( h<=l )
		{
			if(Key.at(l)>= key )
			{
				it = element.begin();
				//it++;
				element.insert(it+l,value);

				it = Key.begin();
				//it++;
				Key.insert(it+l,key);
			}
			else
			{
				it = element.begin();
				it++;
				element.insert(it+l,value);

				it = Key.begin();
				it++;
				Key.insert(it+l,key);
			}
		}
		else
		{
			int mid = ( l + h ) / 2 ;

			if ( Key.at( mid ) == key )	// maybe queue have two element with same Priority 
			{
				it = element.begin();
				//it++;
				element.insert(it+mid,value);

				it = Key.begin();
				//it++;
				Key.insert(it+mid,key);
			} 
		    else if( Key.at( mid ) > key )
			{
				insert(value,key,l,mid-1 );
			}
			else if	( Key.at( mid ) < key )
			{
				insert(value,key,mid+1,h );
				
			}
			
		}
		
	}
public:
	PriorityQueue(const PriorityQueue& Copy)
	{
		Key = Copy.Key;
		element = Copy.element;
		
	}
	PriorityQueue operator=(const PriorityQueue& Copy)
	{
		Key = Copy.Key;
		element = Copy.element;
		return *this;
	}
	PriorityQueue()
	{
	}
	bool empty()
	{
		return element.empty();
	}
	int size()
	{
		return element.size();
	}
	void push(const T& value ,const int& key)
	{
		if(element.empty())
		{
			element.push_back(value);
			Key.push_back(key);
		}
		else
		{
			int s= element.size()-1;
			insert(value,key,0,s);
		}
	}
	T popLowestPriority()
	{
		
		T temp = element.at(0);

		it = element.begin();
		element.erase(it);

		it = Key.begin();
		Key.erase(it);

		return temp ;
	}
	T popHighestPriority()
	{
		
		T temp = element.back();
		element.pop_back();

		Key.pop_back();

		return temp ;
	}
	void changePriority(T value  , int newKey)
	{
		it = element.begin();
		int elementSize = element.size();
		for( int i = 0 ; i < elementSize ; i++ )
		{
			if( element.at( i ) == value )
			{
				element.erase( it+i);

				it = Key.begin();
				Key.erase(it+i);

				this->push(value,newKey);
			}
		}
	}
};	



Example :


Input:
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5
6
7
8
9
10
11
12
13
14
15
16
17
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20
21
22

	PriorityQueue<int> elem;
	elem.push(1,7);
	elem.push(2,1);
	elem.push(3,9);
	elem.push(4,3);
	elem.push(5,6);
	elem.push(8,6);
	
	for( int i = 0 ; !elem.empty() ; i++ )
		cout<<elem.popLowestPriority()<<endl;
	cout<<"-------"<<endl;
	elem.push(1,7);
	elem.push(2,1);
	elem.push(3,9);
	elem.push(4,3);
	elem.push(5,6);
	elem.push(8,6);

	elem.changePriority(8,0);
	for( int i = 0 ; !elem.empty() ; i++ )
		cout<<elem.popLowestPriority()<<endl;


Output :

2
4
8
5
1
3
-------
8
2
4
5
1
3



-----
Sincerely yours,
Sohrab Aboozarkhani Fard
B.S. Student,
Department of Computer Science, "Kharazmi" University , Tehran , Iran.