# Top View Of Binary Tree

Posted: 19 Oct, 2020
Difficulty: Moderate

## PROBLEM STATEMENT

#### You are given a Binary Tree of integers. You are supposed to return the top view of the given binary tree. The Top view of the binary tree is the set of nodes that are visible when we see the tree from the top.

##### Example:
``````For the given binary tree:
``````

``````The top view of the tree will be {10, 4, 2, 1, 3, 6}.
``````
##### Input Format:
``````The first line contains an integer 'T' which denotes the number of test cases.

The first line of each test case contains elements of the tree in the level order form. The line consists of values of nodes separated by a single space. In case a node is null, we take -1 in its place.
``````
##### Example:
``````The input for the tree depicted in the below image would be:

1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1
``````

##### Explanation :
``````Level 1 :
The root node of the tree is 1

Level 2 :
Left child of 1 = 2
Right child of 1 = 3

Level 3 :
Left child of 2 = 4
Right child of 2 = null (-1)
Left child of 3 = 5
Right child of 3 = 6

Level 4 :
Left child of 4 = null (-1)
Right child of 4 = 7
Left child of 5 = null (-1)
Right child of 5 = null (-1)
Left child of 6 = null (-1)
Right child of 6 = null (-1)

Level 5 :
Left child of 7 = null (-1)
Right child of 7 = null (-1)

1
2 3
4 -1 5 6
-1 7 -1 -1 -1 -1
-1 -1
``````
##### Note :
``````1. The first not-null node(of the previous level) is treated as the parent of the first two nodes of the current level. The second not-null node (of the previous level) is treated as the parent node for the next two nodes of the current level and so on.

2. The input ends when all nodes at the last level are null(-1).
``````
##### Output Format:
``````For each test case, return the vector/list of all the elements of the top view of the given tree.
``````
##### Note :
``````You don't need to print the output, it has already been taken care of. Just implement the given function.
``````
##### Constraints:
``````1 <= T <= 100
0 <= N <= 1000
0 <= data <= 10^6 and data != -1

Where ‘N’ is the total number of nodes in the binary tree, and 'data' is the value of the binary tree node.

Time limit: 1 sec
``````