C++ Program to Implement B+ Tree

The B+ tree is a generalization of a binary search tree in that a node can have more than two children. It is basically a self-balancing tree data structure that maintains sorted data and allows sequential access, searches, insertions, and deletions in logarithmic time.

It can be viewed as a B-tree in which each node contains only keys and to which an additional level is added at the bottom with linked leaves.

Algorithm

Begin
   function insert() to insert the nodes into the tree:
      Initialize x as root.
   if x is leaf and having space for one more info then insert a to x.
   else if x is not leaf, do
      Find the child of x that is going to to be traversed next.
   If the child is not full, change x to point to the child.
   If the child is full, split it and change x to point to one of the two parts of the child. If a is smaller
      than mid key in the child, then set x as first part of the child. Else second part of the child.
End

Example Code

#include<iostream>
using namespace std;
struct BplusTree {
   int *d;
   BplusTree **child_ptr;
   bool l;
   int n;
}*r = NULL, *np = NULL, *x = NULL;
BplusTree* init()//to create nodes {
   int i;
   np = new BplusTree;
   np->d = new int[6];//order 6
   np->child_ptr = new BplusTree *[7];
   np->l = true;
   np->n = 0;
   for (i = 0; i < 7; i++) {
      np->child_ptr[i] = NULL;
   }
   return np;
}

void traverse(BplusTree *p)//traverse tree {
   cout<<endl;
   int i;
   for (i = 0; i < p->n; i++) {
      if (p->l == false) {
         traverse(p->child_ptr[i]);
      }
      cout << " " << p->d[i];
   }
   if (p->l == false) {
      traverse(p->child_ptr[i]);
   }
   cout<<endl;
}

void sort(int *p, int n)//sort the tree {
   int i, j, t;
   for (i = 0; i < n; i++) {
      for (j = i; j <= n; j++) {
         if (p[i] >p[j]) {
            t = p[i];
            p[i] = p[j];
            p[j] = t;
         }
      }
   }
}

int split_child(BplusTree *x, int i) {
   int j, mid;
   BplusTree *np1, *np3, *y;
   np3 = init();
   np3->l = true;
   if (i == -1) {
      mid = x->d[2];
      x->d[2] = 0;
      x->n--;
      np1 = init();
      np1->l = false;
      x->l = true;
      for (j = 3; j < 6; j++) {
         np3->d[j - 3] = x->d[j];
         np3->child_ptr[j - 3] = x->child_ptr[j];
         np3->n++;
         x->d[j] = 0;
         x->n--;
      }
      for (j = 0; j < 6; j++) {
         x->child_ptr[j] = NULL;
      }
      np1->d[0] = mid;
      np1->child_ptr[np1->n] = x;
      np1->child_ptr[np1->n + 1] = np3;
      np1->n++;
      r = np1;
   } else {
      y = x->child_ptr[i];
      mid = y->d[2];
      y->d[2] = 0;
      y->n--;
      for (j = 3; j <6 ; j++) {
         np3->d[j - 3] = y->d[j];
         np3->n++;
         y->d[j] = 0;
         y->n--;
      }
      x->child_ptr[i + 1] = y;
      x->child_ptr[i + 1] = np3;
   }
   return mid;
}

void insert(int a) {
   int i, t;
   x = r;
   if (x == NULL) {
      r = init();
      x = r;
   } else {
      if (x->l== true && x->n == 6) {
         t = split_child(x, -1);
         x = r;
         for (i = 0; i < (x->n); i++) {
            if ((a >x->d[i]) && (a < x->d[i + 1])) {
            i++;
            break;
         } else if (a < x->d[0]) {
            break;
         } else {
            continue;
         }
      }
      x = x->child_ptr[i];
   } else {
      while (x->l == false) {
         for (i = 0; i < (x->n); i++) {
            if ((a >x->d[i]) && (a < x->d[i + 1])) {
               i++;
               break;
            } else if (a < x->d[0]) {
               break;
            } else {
               continue;
            }
         }
         if ((x->child_ptr[i])->n == 6) {
            t = split_child(x, i);
            x->d[x->n] = t;
            x->n++;
            continue;
         } else {
            x = x->child_ptr[i];
         }
      }
   }
}
   x->d[x->n] = a;
   sort(x->d, x->n);
   x->n++;
}

int main() {
   int i, n, t;
   cout<<"enter the no of elements to be inserted\n";
   cin>>n;
   for(i = 0; i < n; i++) {
      cout<<"enter the element\n";
      cin>>t;
      insert(t);
   }
   cout<<"traversal of constructed B tree\n";
   traverse(r);
}

Output

enter the no of elements to be inserted
10
enter the element
10
enter the element
20
enter the element
30
enter the element
40
enter the element
50
enter the element
60
enter the element
70
enter the element
80
enter the element
90
enter the element
100
traversal of constructed B tree
10 20
30
40 50
60
70 80 90 100