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Binary Tree Pruning
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20 mins
23 upvotes
Trees
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Binary Tree Pruning

Contributed by
Ankit Kharb
Medium
yellow-spark
0/80
Avg time to solve 20 mins
Success Rate 80 %
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23 upvotes

Problem Statement

You have been given a Binary Tree where the value of each node is either 0 or 1. Your task is to return the same Binary Tree but all of its subtrees that don't contain a 1 have been removed.

Note :

A subtree of a node X is X, plus every node that is a descendant of X.

For Example :

Look at the below example to see a Binary Tree pruning.
Input: [1, 1, 1, 0, 1, 0, 1, 0, 0, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1]

alt text

Output: [1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1]

For example, the input for the tree depicted in the below image would be :

alt text

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)

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.
The input ends when all nodes at the last level are null (-1).

Note :

The above format was just to provide clarity on how the input is formed for a given tree.

The sequence will be put together in a single line separated by a single space. Hence, for the above-depicted tree, the input will be given as:
1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1
Detailed explanation ( Input/output format, Notes, Constraints, Images )
Sample Input 1 :
2
1 -1 0 0 1 -1 -1 -1 -1
0 1 1 0 0 0 -1 -1 -1 1 -1 -1 -1 -1 -1
Sample Output 1 :
1 -1 0 -1 1 -1 -1 
0 1 1 -1 0 -1 -1 1 -1 -1 -1 
Explanation Of Sample Input 1 :
For the first test case, the given binary tree(on left) and the pruned binary tree(on right) are

alt text

Sample Input 2 :
2
0 -1 -1
1 0 -1 -1 -1
Sample Output 2 :
-1
1 -1 -1
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