# Program to print nodes in the Top View of Binary Tree using C++

In this tutorial, we will be discussing a program to print all the nodes that appear in the top view of a given binary tree.

For a particular binary tree, a node appears in its top view if it is the very first node at its horizontal distance. Horizontal distance for the left node of a node x is x-1 and for the right node of node x is x+1.

To solve this, we will do the level order traversal so that we get the topmost node for a particular level before the other nodes present at that level. Further, we will use hashing to check whether the selected node is visible in the top view or not.

## Example

#include <iostream>
#include<queue>
#include<map>
using namespace std;
struct Node{
Node * left;
Node* right;
int h_dist;
int data;
};
Node* create_node(int key){
Node* node=new Node();
node->left = node->right = NULL;
node->data=key;
return node;
}
void print_topview(Node* root){
if(root==NULL)
return;
queue<Node*>q;
map<int,int> m;
int h_dist=0;
root->h_dist=h_dist;
q.push(root);
cout<< "Top View for the given tree:" << endl;
while(q.size()){
h_dist=root->h_dist;
if(m.count(h_dist)==0)
m[h_dist]=root->data;
if(root->left){
root->left->h_dist=h_dist-1;
q.push(root->left);
}
if(root->right){
root->right->h_dist=h_dist+1;
q.push(root->right);
}
q.pop();
root=q.front();
}
for(auto i=m.begin();i!=m.end();i++){
cout<<i->second<< " ";
}
}
int main(){
Node* root = create_node(11);
root->left = create_node(23);
root->right = create_node(35);
root->left->right = create_node(47);
root->left->right->right = create_node(59);
root->left->right->right->right = create_node(68);
print_topview(root);
return 0;
}

## Output

Top View for the given tree:
23 11 35 68

Updated on: 01-Nov-2019

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