STL Sample for the heap Functions

• The Standard C++ Library included with: - Microsoft Visual C++, 32-bit Edition, version 4.2

SUMMARY

The sample code below illustrates how to use the make_heap, sort_heap, push_heap, pop_heap, begin, and end STL functions in Visual C++.

MORE INFORMATION

Required Header

   <algorithm>

Prototype

   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)

Description

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 functions converts the range [first..last) into a heap.

The sort_heap function sorts a "heapified" 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), then reduces the length of the sequence by one before restoring the heap property.

The non-predicate versions of the heap functions use the operator< for comparisons.

Sample Code

//////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
// heap_functions.cpp : Illustrates how to use the
//                      make_heap, sort_heap, push_heap
//                      and pop_heap functions.
//
// 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
//
// Written by Kalindi Sanghrajka
// of Microsoft Product Support Services,
// Software Core Developer Support.
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
//////////////////////////////////////////////////////////////////////

// disable warning C4786: symbol greater than 255 character,
// okay to ignore

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

void main()

    const int VECTOR_SIZE = 8 ;

    // Define a template class vector of int
    typedef vector<int, allocator<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 ;

Program Output is:

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 }

REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.