Implementation of Binomial Heap

In previous article, we have discussed about the concepts related to Binomial heap.

Examples Binomial Heap:


12------------10--------------------20
             /  \                 /  | \
           15    50             70  50  40
           |                  / |    |     
           30               80  85  65 
                            |
                           100
A Binomial Heap with 13 nodes. It is a collection of 3 
Binomial Trees of orders 0, 2 and 3 from left to right. 

    10--------------------20
   /  \                 /  | \
 15    50             70  50  40
 |                  / |    |     
 30               80  85  65 
                  |
                 100

In this article, implementation of Binomial Heap is discussed. Following functions implemented :

  1. insert(H, k): Inserts a key ‘k’ to Binomial Heap ‘H’. This operation first creates a Binomial Heap with single key ‘k’, then calls union on H and the new Binomial heap.
  2. getMin(H): A simple way to getMin() is to traverse the list of root of Binomial Trees and return the minimum key. This implementation requires O(Logn) time. It can be optimized to O(1) by maintaining a pointer to minimum key root.
  3. extractMin(H): This operation also uses union(). We first call getMin() to find the minimum key Binomial Tree, then we remove the node and create a new Binomial Heap by connecting all subtrees of the removed minimum node. Finally we call union() on H and the newly created Binomial Heap. This operation requires O(Logn) time.
// C++ program to implement different operations
// on Binomial Heap
#include<bits/stdc++.h>
using namespace std;

// A Binomial Tree node.
struct Node
{
    int data, degree;
    Node *child, *sibling, *parent;
};

Node* newNode(int key)
{
    Node *temp = new Node;
    temp->data = key;
    temp->degree = 0;
    temp->child = temp->parent = temp->sibling = NULL;
    return temp;
}

// This function merge two Binomial Trees.
Node* mergeBinomialTrees(Node *b1, Node *b2)
{
    // Make sure b1 is smaller
    if (b1->data > b2->data)
        swap(b1, b2);

    // We basically make larger valued tree
    // a child of smaller valued tree
    b2->parent = b1;
    b2->sibling = b1->child;
    b1->child = b2;
    b1->degree++;

    return b1;
}

// This function perform union operation on two
// binomial heap i.e. l1 & l2
list<Node*> unionBionomialHeap(list<Node*> l1,
                               list<Node*> l2)
{
    // _new to another binomial heap which contain
    // new heap after merging l1 & l2
    list<Node*> _new;
    list<Node*>::iterator it = l1.begin();
    list<Node*>::iterator ot = l2.begin();
    while (it!=l1.end() && ot!=l2.end())
    {
        // if D(l1) <= D(l2)
        if((*it)->degree <= (*ot)->degree)
        {
            _new.push_back(*it);
            it++;
        }
        // if D(l1) > D(l2)
        else
        {
            _new.push_back(*ot);
            ot++;
        }
    }

    // if there remains some elements in l1
    // binomial heap
    while (it != l1.end())
    {
        _new.push_back(*it);
        it++;
    }

    // if there remains some elements in l2
    // binomial heap
    while (ot!=l2.end())
    {
        _new.push_back(*ot);
        ot++;
    }
    return _new;
}

// adjust function rearranges the heap so that
// heap is in increasing order of degree and
// no two binomial trees have same degree in this heap
list<Node*> adjust(list<Node*> _heap)
{
    if (_heap.size() <= 1)
        return _heap;
    list<Node*> new_heap;
    list<Node*>::iterator it1,it2,it3;
    it1 = it2 = it3 = _heap.begin();

    if (_heap.size() == 2)
    {
        it2 = it1;
        it2++;
        it3 = _heap.end();
    }
    else
    {
        it2++;
        it3=it2;
        it3++;
    }
    while (it1 != _heap.end())
    {
        // if only one element remains to be processed
        if (it2 == _heap.end())
            it1++;

        // If D(it1) < D(it2) i.e. merging of Binomial
        // Tree pointed by it1 & it2 is not possible
        // then move next in heap
        else if ((*it1)->degree < (*it2)->degree)
        {
            it1++;
            it2++;
            if(it3!=_heap.end())
                it3++;
        }

        // if D(it1),D(it2) & D(it3) are same i.e.
        // degree of three consecutive Binomial Tree are same
        // in heap
        else if (it3!=_heap.end() &&
                (*it1)->degree == (*it2)->degree &&
                (*it1)->degree == (*it3)->degree)
        {
            it1++;
            it2++;
            it3++;
        }

        // if degree of two Binomial Tree are same in heap
        else if ((*it1)->degree == (*it2)->degree)
        {
            Node *temp;
            *it1 = mergeBinomialTrees(*it1,*it2);
            it2 = _heap.erase(it2);
            if(it3 != _heap.end())
                it3++;
        }
    }
    return _heap;
}

// inserting a Binomial Tree into binomial heap
list<Node*> insertATreeInHeap(list<Node*> _heap,
                              Node *tree)
{
    // creating a new heap i.e temp
    list<Node*> temp;

    // inserting Binomial Tree into heap
    temp.push_back(tree);

    // perform union operation to finally insert
    // Binomial Tree in original heap
    temp = unionBionomialHeap(_heap,temp);

    return adjust(temp);
}

// removing minimum key element from binomial heap
// this function take Binomial Tree as input and return
// binomial heap after
// removing head of that tree i.e. minimum element
list<Node*> removeMinFromTreeReturnBHeap(Node *tree)
{
    list<Node*> heap;
    Node *temp = tree->child;
    Node *lo;

    // making a binomial heap from Binomial Tree
    while (temp)
    {
        lo = temp;
        temp = temp->sibling;
        lo->sibling = NULL;
        heap.push_front(lo);
    }
    return heap;
}

// inserting a key into the binomial heap
list<Node*> insert(list<Node*> _head, int key)
{
    Node *temp = newNode(key);
    return insertATreeInHeap(_head,temp);
}

// return pointer of minimum value Node
// present in the binomial heap
Node* getMin(list<Node*> _heap)
{
    list<Node*>::iterator it = _heap.begin();
    Node *temp = *it;
    while (it != _heap.end())
    {
        if ((*it)->data < temp->data)
            temp = *it;
        it++;
    }
    return temp;
}

list<Node*> extractMin(list<Node*> _heap)
{
    list<Node*> new_heap,lo;
    Node *temp;

    // temp contains the pointer of minimum value
    // element in heap
    temp = getMin(_heap);
    list<Node*>::iterator it;
    it = _heap.begin();
    while (it != _heap.end())
    {
        if (*it != temp)
        {
            // inserting all Binomial Tree into new
            // binomial heap except the Binomial Tree
            // contains minimum element
            new_heap.push_back(*it);
        }
        it++;
    }
    lo = removeMinFromTreeReturnBHeap(temp);
    new_heap = unionBionomialHeap(new_heap,lo);
    new_heap = adjust(new_heap);
    return new_heap;
}

// print function for Binomial Tree
void printTree(Node *h)
{
    while (h)
    {
        cout << h->data << " ";
        printTree(h->child);
        h = h->sibling;
    }
}

// print function for binomial heap
void printHeap(list<Node*> _heap)
{
    list<Node*> ::iterator it;
    it = _heap.begin();
    while (it != _heap.end())
    {
        printTree(*it);
        it++;
    }
}


// Driver program to test above functions
int main()
{
    int ch,key;
    list<Node*> _heap;

    // Insert data in the heap
    _heap = insert(_heap,10);
    _heap = insert(_heap,20);
    _heap = insert(_heap,30);

    cout << "Heap elements after insertion:\n";
    printHeap(_heap);

    Node *temp = getMin(_heap);
    cout << "\nMinimum element of heap "
         << temp->data << "\n";

    // Delete minimum element of heap
    _heap = extractMin(_heap);
    cout << "Heap after deletion of minimum element\n";
    printHeap(_heap);

    return 0;
}

Output:

Heap elements after insertion:
30 10 20 
Minimum element of heap 10
Heap after deletion of minimum element
20 30 

This article is contributed by Sahil Chhabra (akku) and Arun Mittal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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