sum_of_binary_tree.cpp

// iterative approach. solved using Level order Traversal. Time Complexity O(n)  where n are number of nodes in tree. Space Complexity:- O(n) where n are number of nodes in tree
long int sumBT(Node* root)
{
if(root == NULL)
return 0;
long int sum=0;
queue<Node*> q;
q.push(root);
while(!q.empty())
{
    Node* temp = q.front();
    sum=sum+temp->key;
    q.pop();
    if(temp->left)
        q.push(temp->left);
    if(temp->right)
        q.push(temp->right);
}
return sum;    
} 
// recursive approach Time complexity=O(n) 
long int sumBT(Node* root)
{
if(root == NULL)
    return 0;

long int a = sumBT(root->left);
long int b = sumBT(root ->right);
return root ->key +a +b;
    
}