# Complete Binary Tree Inserter in C++

C++Server Side ProgrammingProgramming

As we know a complete binary tree is a binary tree in which every level, except possibly the last, is completely filled, and all nodes are as far left as possible. We have to write a data structure CBTInserter that is initialized with a complete binary tree and it supports the following operations−

• CBTInserter(TreeNode root) this initializes the data structure on a given tree with head node root;

• CBTInserter.insert(int v) this will used to insert a TreeNode into the tree with value node.val = v so that the tree remains complete, and returns the value of the parent of the inserted TreeNode;

• CBTInserter.get_root() this will return the head node of the tree.

So for example, if we initialize the tree as [1,2,3,4,5,6], then insert 7 and 8, then try to get the tree, the output will be: 3, 4,[1,2,3,4,5,6,7,8], the 3 is because 7 will be inserted under 3, and 4 is because 8 will be inserted under 4.

To solve this, we will follow these steps −

• Define a queue q, and a root

• The initializer will take the full binary tree, then work as follows

• set root as given root, insert root into the q

• while true −

• if left of root is present, then insert left of root into q, otherwise break the loop

• if right of root is present, then insert right of root into q and delete front node from q, otherwise break the loop

• From the insert method, it will take the value v

• set parent := front element of q, temp := new node with value v, and insert it into q

• if left of parent is not present, then set left of parent := temp otherwise delete front element from q, and insert temp as right child of parent

• return the value of parent

• from the getRoot() method, return the root

## Example

Let us see the following implementation to get better understanding −

class CBTInserter {
public:
queue <TreeNode*> q;
TreeNode* root;
CBTInserter(TreeNode* root) {
this->root = root;
q.push(root);
while(1){
if(root->left){
q.push(root->left);
}
else break;
if(root->right){
q.push(root->right);
q.pop();
root = q.front();
}
else break;
}
}
int insert(int v) {
TreeNode* parent = q.front();
TreeNode* temp = new TreeNode(v);
q.push(temp);
if(!parent->left){
parent->left = temp;
} else {
q.pop();
parent->right = temp;
}
return parent->val;
}
TreeNode* get_root() {
return root;
}
};

## Input

["CBTInserter","insert","insert","get_root"]
[[[1,2,3,4,5,6]],[7],[8],[]]

## Output

[null,3,4,[1,2,3,4,5,6,7,8]]
Published on 17-Mar-2020 06:37:33