B-Tree.cpp

/*
 * C++ Program to Implement B-Tree
 */
#include <iostream>
using namespace std;

// A BTree node
class BTreeNode
{
    private:
        int *keys;
        int t;
        BTreeNode **C;
        int n;
        bool leaf;
    public:
        BTreeNode(int t1, bool leaf1)
        {
            t = t1;
            leaf = leaf1;
            keys = new int[2*t-1];
            C = new BTreeNode *[2*t];
            n = 0;
        }
        // traverse all nodes in a subtree rooted with this node
        void traverse()
        {
            int i;
            for (i = 0; i < n; i++)
            {
                if (leaf == false)
                    C[i]->traverse();
                cout << " " << keys[i];
            }
            if (leaf == false)
                C[i]->traverse();
        }
        void insertNonFull(int k)
        {
            int i = n-1;
            if (leaf == true)
            {
                while (i >= 0 && keys[i] > k)
                {
                    keys[i+1] = keys[i];
                    i--;
                }
                keys[i+1] = k;
                n = n+1;
            }
            else
            {
                while (i >= 0 && keys[i] > k)
                    i--;
                if (C[i+1]->n == 2*t-1)
                {
                    splitChild(i+1, C[i+1]);
                    if (keys[i+1] < k)
                        i++;
                }
                C[i+1]->insertNonFull(k);
            }
        }
        void splitChild(int i, BTreeNode *y)
        {
            BTreeNode *z = new BTreeNode(y->t, y->leaf);
            z->n = t - 1;
            for (int j = 0; j < t-1; j++)
                z->keys[j] = y->keys[j+t];
            if (y->leaf == false)
            {
                for (int j = 0; j < t; j++)
                    z->C[j] = y->C[j+t];
            }
            y->n = t - 1;
            for (int j = n; j >= i+1; j--)
                C[j+1] = C[j];
            C[i+1] = z;
            for (int j = n-1; j >= i; j--)
                keys[j+1] = keys[j];
            keys[i] = y->keys[t-1];
            n = n + 1;
        }
        BTreeNode *search(int k)
        {
            int i = 0;
            while (i < n && k > keys[i])
                i++;
            if (keys[i] == k)
                return this;
            if (leaf == true)
                return NULL;
            return C[i]->search(k);
        }
        friend class BTree;
};

// Class BTree
class BTree
{
    private:
        BTreeNode *root;
        int t;
    public:
        BTree(int _t)
        {
            root = NULL;
            t = _t;
        }
        void traverse()
        {
            if (root != NULL)
                root->traverse();
        }
        BTreeNode* search(int k)
        {
            return (root == NULL)? NULL : root->search(k);
        }
        void insert(int k)
        {
            if (root == NULL)
            {
                root = new BTreeNode(t, true);
                root->keys[0] = k;
                root->n = 1;
            }
            else
            {
                if (root->n == 2*t-1)
                {
                    BTreeNode *s = new BTreeNode(t, false);
                    s->C[0] = root;
                    s->splitChild(0, root);
                    int i = 0;
                    if (s->keys[0] < k)
                        i++;
                    s->C[i]->insertNonFull(k);
                    root = s;
                }
                else
                    root->insertNonFull(k);
            }
        }
};
// Main
int main()
{
    BTree t(3);
    t.insert(10);
    t.insert(20);
    t.insert(5);
    t.insert(6);
    t.insert(12);
    t.insert(30);
    t.insert(7);
    t.insert(17);
    cout << "Traversal of the constucted tree is ";
    t.traverse();
    cout<<endl;
    int k = 6;
    cout<<k<<" is ";
    (t.search(k) != NULL)? cout << "Present\n" : cout << "Not Present\n";
    k = 15;
    cout<<k<<" is ";
    (t.search(k) != NULL)? cout << "Present\n" : cout << "Not Present\n";
    return 0;
}