heap

Illustrates how to use the heap Standard Template Library (STL) functions in Visual C++.

template<class RandomAccessIterator> inline 
   void make_heap( 
      RandomAccessIterator First, 
      RandomAccessIterator Last 
   ) 
template<class RandomAccessIterator> inline 
   void sort_heap( 
      RandomAccessIterator First, 
      RandomAccessIterator Last 
   ) 
template<class RandomAccessIterator> inline 
   void push_heap( 
      RandomAccessIterator First, 
      RandomAccessIterator Last 
   ) 
template<class RandomAccessIterator> inline 
   void pop_heap( 
      RandomAccessIterator First, 
      RandomAccessIterator Last 
   )

Remarks

A heap is a sequence of elements organized like a binary tree. Each heap element corresponds to a tree node. The first value in the sequence [First..Last) is the root and is the largest value in the heap. Every element in the heap satisfies the following: Every element is less than or equal to its parent. The largest element is stored in the root, and all children hold progressively smaller values. The make_heap function converts the range [First..Last) into a heap. The sort_heap function sorts a sequence that was created using the make_heap function. The push_heap function inserts a new value into the heap. The pop_heap function swaps the first and last elements in the heap specified by [First, Last), and then reduces the length of the sequence by one before restoring the heap property. The nonpredicate versions of the heap functions use operator< for comparisons.

Example

// heapfunc.cpp
// compile with: /EHsc
// 
// Functions:
//    make_heap : convert a sequence to a heap
//    sort_heap : sort a heap
//    push_heap : insert an element in a heap
//    pop_heap  : remove the top element from a heap

// disable warning C4786: symbol greater than 255 characters,
// okay to ignore
#pragma warning(disable: 4786)

#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>

using namespace std;

int main()
{
    const int VECTOR_SIZE = 8 ;

    // Define a template class vector of int
    typedef vector<int > IntVector ;

    //Define an iterator for template class vector of strings
    typedef IntVector::iterator IntVectorIt ;

    IntVector Numbers(VECTOR_SIZE) ;

    IntVectorIt it ;

    // Initialize vector Numbers
    Numbers[0] = 4 ;
    Numbers[1] = 10;
    Numbers[2] = 70 ;
    Numbers[3] = 10 ;
    Numbers[4] = 30 ;
    Numbers[5] = 69 ;
    Numbers[6] = 96 ;
    Numbers[7] = 100;

    // print content of Numbers
    cout << "Numbers { " ;
    for(it = Numbers.begin(); it != Numbers.end(); it++)
        cout << *it << " " ;
    cout << " }\n" << endl ;

    // convert Numbers into a heap
    make_heap(Numbers.begin(), Numbers.end()) ;

    cout << "After calling make_heap\n" << endl ;

    // print content of Numbers
    cout << "Numbers { " ;
    for(it = Numbers.begin(); it != Numbers.end(); it++)
        cout << *it << " " ;
    cout << " }\n" << endl ;

    // sort the heapified sequence Numbers
    sort_heap(Numbers.begin(), Numbers.end()) ;

    cout << "After calling sort_heap\n" << endl ;

    // print content of Numbers
    cout << "Numbers { " ;
    for(it = Numbers.begin(); it != Numbers.end(); it++)
        cout << *it << " " ;
    cout << " }\n" << endl ;

    //insert an element in the heap
    Numbers.push_back(7) ;
    push_heap(Numbers.begin(), Numbers.end()) ;

    // you need to call make_heap to re-assert the
    // heap property
    make_heap(Numbers.begin(), Numbers.end()) ;

    cout << "After calling push_heap and make_heap\n" << endl ;

    // print content of Numbers
    cout << "Numbers { " ;
    for(it = Numbers.begin(); it != Numbers.end(); it++)
        cout << *it << " " ;
    cout << " }\n" << endl ;

    // remove the root element from the heap Numbers
    pop_heap(Numbers.begin(), Numbers.end()) ;

    cout << "After calling pop_heap\n" << endl ;

    // print content of Numbers
    cout << "Numbers { " ;
    for(it = Numbers.begin(); it != Numbers.end(); it++)
        cout << *it << " " ;
    cout << " }\n" << endl ;
}

Output

Numbers { 4 10 70 10 30 69 96 100  }

After calling make_heap

Numbers { 100 30 96 10 4 69 70 10  }

After calling sort_heap

Numbers { 4 10 10 30 69 70 96 100  }

After calling push_heap and make_heap

Numbers { 100 69 96 30 4 70 10 10 7  }

After calling pop_heap

Numbers { 96 69 70 30 4 7 10 10 100  }

Requirements

Header: <algorithm>

See Also

Concepts

Standard Template Library Samples