## Algorithm

Problem Name: Data Structures - Tree : Top View

In this HackerRank in Data Structures - Tree : Top View solutions

Given a pointer to the root of a binary tree, print the top view of the binary tree.

The tree as seen from the top the nodes, is called the top view of the tree.

For example :

``````   1
\
2
\
5
/  \
3    6
\
4
``````

Top View : 1- > 2- > 5- > 6

Complete the function topView and print the resulting values on a single line separated by space.

Input Format

You are given a function,

``````void topView(node * root) {

}
``````

Constraints

1 <= Nodes in the tree <= 500

Output Format

Print the values on a single line separated by space.

Sample Input

``````   1
\
2
\
5
/  \
3    6
\
4
``````

Sample Output

1 2 5 6

Explanation

``````   1
\
2
\
5
/  \
3    6
\
4
``````
From the top, only nodes 1,2,5,6 are visible.

## Code Examples

### #1 Code Example with C Programming

```Code - C Programming```

``````
#include <stdio.h>
#include <string.h>
#include  < math.h>
#include <stdlib.h>

struct node {

int data;
struct node *left;
struct node *right;

};

struct node* insert( struct node* root, int data ) {

if(root == NULL) {

struct node* node = (struct node*)malloc(sizeof(struct node));

node->data = data;

node->left = NULL;
node->right = NULL;
return node;

} else {

struct node* cur;

if(data  < = root->data) {
cur = insert(root->left, data);
root->left = cur;
} else {
cur = insert(root->right, data);
root->right = cur;
}

return root;
}
}

/* you only have to complete the function given below.
node is defined as

struct node {

int data;
struct node *left;
struct node *right;

};

*/
typedef struct node node;

void traverse(int *topL, int *topR, int lpos, int rpos, node *n){
if(!n) return;
if(lpos >= 0 && topL[lpos] == 0) topL[lpos] = n->data;
traverse(topL, topR, lpos + 1, rpos - 1, n->left);
traverse(topL, topR, lpos - 1, rpos + 1, n->right);
if (rpos >= 0) topR[rpos] = n->data;
}

void topView(struct node *root) {
if(!root) return;
int left[501];
int right[501];
memset(left, 0, sizeof(int) * 501);
memset(right, 0, sizeof(int) * 501);

//traverse the tree
traverse(left, right, -1, 0, root);

int i = 0;
while(left[i] > 0) i++;
for(i--; i >= 0; i--) printf("%d ", left[i]);
for(i = 0; right[i] > 0; i++) printf("%d ", right[i]);
}

int main() {

struct node* root = NULL;

int t;
int data;

scanf("%d", &t);

while(t-- > 0) {
scanf("%d", &data);
root = insert(root, data);
}

topView(root);
return 0;
}
``````
Copy The Code &

### #2 Code Example with C++ Programming

```Code - C++ Programming```

``````
#include<bits/stdc++.h>

using namespace std;

class Node {
public:
int data;
Node *left;
Node *right;
Node(int d) {
data = d;
left = NULL;
right = NULL;
}
};

class Solution {
public:
Node* insert(Node* root, int data) {
if(root == NULL) {
return new Node(data);
} else {
Node* cur;
if(data  < = root->data) {
cur = insert(root->left, data);
root->left = cur;
} else {
cur = insert(root->right, data);
root->right = cur;
}

return root;
}
}

/*
class Node {
public:
int data;
Node *left;
Node *right;
Node(int d) {
data = d;
left = NULL;
right = NULL;
}
};

*/

void topView(Node * root) {
queue < pair<int,Node*>> q; q.push(make_pair(0,root));
map < int,Node*> ans;
for(auto i=q.front();!q.empty();q.pop(),i=q.front()){
if(!i.second) continue;
ans.insert(i);
q.push(make_pair(i.first+1,i.second->right));
q.push(make_pair(i.first-1,i.second->left));
}
for(auto i:ans) cout<<i.second->data<<" ";
}

}; //End of Solution

int main() {

Solution myTree;
Node* root = NULL;

int t;
int data;

std::cin >> t;

while(t-- > 0) {
std::cin >> data;
root = myTree.insert(root, data);
}

myTree.topView(root);
return 0;
}
``````
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### #3 Code Example with Java Programming

```Code - Java Programming```

``````
import java.util.*;
import java.io.*;

class Node {
Node left;
Node right;
int data;

Node(int data) {
this.data = data;
left = null;
right = null;
}
}

class Solution {

/*

class Node
int data;
Node left;
Node right;
*/
static class Pair{
public Node node;
public int dist;

public Pair(Node node, int dist){
this.node = node;
this.dist = dist;
}
}

public static void topView(Node root) {
if(root == null)
return;
Map < Integer, Integer> mp = new TreeMap<>();
while(!q.isEmpty()){
Pair pair = q.poll();
Node node = pair.node;
int dist = pair.dist;
if(!mp.containsKey(dist)){
mp.put(dist, node.data);
}
if(node.left != null){
}
if(node.right != null){
}
}
for(Map.Entry < Integer, Integer> ent : mp.entrySet()){
System.out.print(ent.getValue()+ " ");
}
}

public static Node insert(Node root, int data) {
if(root == null) {
return new Node(data);
} else {
Node cur;
if(data <= root.data) {
cur = insert(root.left, data);
root.left = cur;
} else {
cur = insert(root.right, data);
root.right = cur;
}
return root;
}
}

public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int t = scan.nextInt(>;
Node root = null;
while(t-- > 0) {
int data = scan.nextInt();
root = insert(root, data);
}
scan.close();
topView(root);
}
}
``````
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### #4 Code Example with Python Programming

```Code - Python Programming```

``````
class Node:
def __init__(self, info):
self.info = info
self.left = None
self.right = None
self.level = None

def __str__(self):
return str(self.info)

class BinarySearchTree:
def __init__(self):
self.root = None

def create(self, val):
if self.root == None:
self.root = Node(val)
else:
current = self.root

while True:
if val < current.info:
if current.left:
current = current.left
else:
current.left = Node(val)
break
elif val > current.info:
if current.right:
current = current.right
else:
current.right = Node(val)
break
else:
break

"""
Node is defined as
self.left (the left child of the node)
self.right (the right child of the node)
self.info (the value of the node)
"""
def topView(root):
hm={}
queue=[]
queue.append((root,0))
while(queue):
q=queue.pop(0)
if q[1] not in hm:
hm[q[1]]=q[0].info
if q[0].left:
queue.append((q[0].left,q[1]-1))
if q[0].right:
queue.append((q[0].right,q[1]+1))
for k, v in sorted(hm.items()):
print(str(v)+' ', end='')

tree = BinarySearchTree()
t = int(input())

arr = list(map(int, input().split()))

for i in range(t):
tree.create(arr[i])

topView(tree.root)
``````
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