make_heap() in C++ STL

The C++ Standard Library consists of the header, <algorithm> which defines a collection of functions (principally designed to deal with a range of elements). make_heap() is a method in the STL that rearranges the elements in a given range in such a way that they form a heap.

Syntax:

make_heap( iterator_begin, iterator_end, comparator ); //comparator is optional

Parameters: The make_heap() method accepts 3 parameters

• iterator_begin: Iterator to the initial position of new heap
• iterator_end: Iterator to the final position of new heap ( Note: the range is [iterator_begin,iterator_end) )
• comparator: Binary function that accepts two elements in the range as arguments, and returns a value convertible to bool.

Return value: none

Example of make_heap() method

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

using namespace std;

void print(vector<int> v)
{
    vector<int>::iterator it;
    for(it = v.begin(); it !=v.end(); ++it)
        cout<< *it <<"  ";
    cout<<endl;
}

int main()
{
    vector<int> v;
    v.push_back(4);
    v.push_back(3);
    v.push_back(8);
    v.push_back(-5);
    v.push_back(7);


    cout<<"Before heap: "<<endl;
    print(v);

    make_heap(v.begin(), v.end());
    cout<<"After heap: "<<v.front()<<endl;
    print(v);

    make_heap(v.begin(), v.end(), greater<int>()); //creates a min heap
    cout<<"After heap: "<<v.front()<<endl;
    print(v);
}

Output:

Before heap: 
4  3  8  -5  7
After heap: 
8  7  4  -5  3
After heap: 
-5  3  4  7  8