C++/Queue Stack/priority queue

A priority_queue: size(), top(), empty(), pop()

<source lang="cpp">

1. include <queue>
2. include <iostream>

int main () {

   using namespace std;
   priority_queue <int> pqIntegers;
   pqIntegers.push (10);
   pqIntegers.push (5);
   pqIntegers.push (-1);
   pqIntegers.push (20);
   cout << "The queue contains " << pqIntegers.size () << " elements";
   cout << endl;
   cout << "Element at the top: " << pqIntegers.top () << endl << endl;
   while (!pqIntegers.empty ())
   {
       cout << "Deleting the topmost element: " << pqIntegers.top ();
       cout << endl;
       pqIntegers.pop ();
   }
   return 0;

}

 </source>

Define your function to Prioritize a priority_queue

<source lang="cpp">

1. include <iostream>
2. include <string>
3. include <queue>

using namespace std; class Prioritize { public:

    int operator() ( const pair<string, unsigned int>& p1,const pair<string, unsigned int>& p2 ) {
        return p1.second < p2.second;
    }

}; int main() {

    priority_queue< pair< string, unsigned int >,vector <pair< string, unsigned int > >, Prioritize >   pq;
    pq.push( pair<string, int>( "A", 2) );
    pq.push( pair<string, int>( "B", 10 ) );
    pq.push( pair<string, int>( "C", 1 ) );
    while ( !pq. empty() ) {
        cout << pq.top().first << endl;
        pq.pop();
    }
    return 0;

}

 </source>

priority_queue of double

<source lang="cpp">

1. include <iostream>

using std::cout; using std::endl;

1. include <queue>

int main() {

  std::priority_queue< double > priorities;
  
  priorities.push( 3.2 );
  priorities.push( 9.8 );
  priorities.push( 5.4 );
  cout << "Popping from priorities: ";
  
  while ( !priorities.empty() ) 
  {
     cout << priorities.top() << " ";
     priorities.pop();
  }
  cout << endl;
  return 0;

}

/* 

Popping from priorities: 9.8 5.4 3.2

*/       
   
   
 </source>

Priority Queue Opertions: empty(), pop(), top(), push()

<source lang="cpp">

1. include <iostream>
2. include <string>
3. include <queue>

using namespace std; class Prioritize { public:

    int operator() ( const pair<string, unsigned int>& p1,const pair<string, unsigned int>& p2 ) {
        return p1.second < p2.second;
    }

}; int main() {

    priority_queue< pair< string, unsigned int >,vector <pair< string, unsigned int > >, Prioritize >   pq;
    pq.push( pair<string, int>( "A", 2) );
    pq.push( pair<string, int>( "B", 10 ) );
    pq.push( pair<string, int>( "C", 1 ) );
    while ( !pq. empty() ) {
        cout << pq.top().first << endl;
        pq.pop();
    }
    return 0;

}

 </source>

priority_queue: pop

<source lang="cpp">

1. include <iostream>
2. include <queue>

using namespace std; int main() {

 int thedata[] = {45, 34, 56, 27, 71, 50, 62};
 priority_queue<int> pq;  
 cout << "The priority_queue size is now " << pq.size() << endl;
 
 cout << "Pushing 4 elements " << endl;
 for (int i = 0; i < 4; ++i)
   pq.push(thedata[i]);
 cout << "The priority_queue size is now " << pq.size() << endl;
 cout << "Popping 3 elements " << endl;
 for (int i = 0; i < 3; ++i) {
   cout << pq.top() << endl;
   pq.pop();
 }
 cout << "The priority_queue size is now " << pq.size() << endl;
 return 0;

}

/* 

The priority_queue size is now 0 Pushing 4 elements The priority_queue size is now 4 Popping 3 elements 56 45 34 The priority_queue size is now 1

*/       
   
   
 </source>

priority_queue: push and size

<source lang="cpp">

1. include <iostream>
2. include <queue>

using namespace std; int main() {

 int thedata[] = {45, 34, 56, 27, 71, 50, 62};
 priority_queue<int> pq;  
 cout << "The priority_queue size is now " << pq.size() << endl;
 
 cout << "Pushing 4 elements " << endl;
 for (int i = 0; i < 4; ++i)
   pq.push(thedata[i]);
 cout << "The priority_queue size is now " << pq.size() << endl;
 return 0;

}

/* 

The priority_queue size is now 0 Pushing 4 elements The priority_queue size is now 4

*/       
   
   
 </source>

priority_queue: push, pop, top, empty

<source lang="cpp">

/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <queue>

using namespace std; int main() {

   priority_queue<float> q;
   // insert three elements into the priority queue
   q.push(66.6);
   q.push(22.2);
   q.push(44.4);
   // read and print two elements
   cout << q.top() << " ";
   q.pop();
   cout << q.top() << endl;
   q.pop();
   // insert three more elements
   q.push(11.1);
   q.push(55.5);
   q.push(33.3);
   // skip one element
   q.pop();
   // pop and print remaining elements
   while (!q.empty()) {
       cout << q.top() << " ";
       q.pop();
   }
   cout << endl;

} /* 66.6 44.4 33.3 22.2 11.1

*/
       
   
   
 </source>

priority_queue: top

<source lang="cpp">

1. include <iostream>
2. include <queue>

using namespace std; int main() {

 int thedata[] = {45, 34, 56, 27, 71, 50, 62};
 priority_queue<int> pq;  
 cout << "The priority_queue size is now " << pq.size() << endl;
 
 cout << "Pushing 4 elements " << endl;
 for (int i = 0; i < 4; ++i)
   pq.push(thedata[i]);
 cout << "The priority_queue size is now " << pq.size() << endl;
 cout << "Popping 3 elements " << endl;
 for (int i = 0; i < 3; ++i) {
   cout << pq.top() << endl;
   pq.pop();
 }
 cout << "The priority_queue size is now " << pq.size() << endl;

 cout << "Popping all elements" << endl;
 while (!pq.empty()) {
   cout << pq.top() << endl;
   pq.pop();
 } 
 cout << "The priority_queue size is now " << pq.size() << endl;
 return 0;

}

/* 

The priority_queue size is now 0 Pushing 4 elements The priority_queue size is now 4 Popping 3 elements 56 45 34 The priority_queue size is now 1 Popping all elements 27 The priority_queue size is now 0

*/       
   
   
 </source>

Using a Priority Queue

<source lang="cpp">

1. include <iostream>
2. include <queue>
3. include <string>

using namespace std; class Message {

  public:
  Message( string message = "A",string source = "B", int security_level = 0 );
  bool operator<( const Message& rhs ) const;
  string message() const;
  int security_level() const;
  string source() const;
  private:
  string message_, source_;
  int security_level_;

}; inline Message::Message( string message, string source, int security_level )

  : message_( message ), source_( source ),
    security_level_( security_level )

{} bool Message::operator<( const Message& rhs ) const { return security_level() < rhs.security_level(); } string Message::message() const { return message_; } string Message::source() const { return source_; } int Message::security_level() const { return security_level_; } int main( ) {

  const char* message[] = { "A","B", "C","D","E","F","G" };
  const char* source[] = { "a", "b", "c","d", "e", "f", "G" };
  const int security_level[] = { 0, 1, 3, 2, 6, 7, 8 };
  const int num_messages = sizeof( security_level ) / sizeof( security_level[0] );
  priority_queue<Message> messages;
  for( int i = 0; i < num_messages; ++i ){
     cout << "Event " << (i+1) << ": Security level - "
        << security_level[i] << "\n\t" << source[i] << " reports "
        << message[i] << endl;
     messages.push( Message( message[i], source[i],security_level[i] ) );
  }
  while( !messages.empty() )
  {
     cout << "Security level - "
        << messages.top().security_level() << "\n\t"
        << messages.top().source() << " reports "
        << messages.top().message() << endl;
     messages.pop();
  }

}

 </source>