Question

We are given the head node root of a binary tree, where additionally every node's value is either a 0 or a 1. Return the same tree where every subtree (of the given tree) not containing a 1 has been removed. (Recall that the subtree of a node X is X, plus every node that is a descendant of X.)

Answer 1

The question involves pruning a binary tree in computer science to remove all subtrees that do not contain a node with the value 1. The solution involves a recursive approach to retain only the relevant subtrees.

Step-by-step explanation:

The student's question pertains to a binary tree data structure in computer science. Specifically, the question is about pruning a binary tree such that only the subtrees containing at least one node with a value of 1 are left intact. Here is how you could approach solving this problem:

Step-by-step Algorithm

1. Define a recursive function that takes a node of the binary tree as an argument.
2. When the current node is null, return null, as it signifies the end of a branch and no further action is required.
3. If the current node is not null, recursively call the function for the left and right subtrees. Set the returned node from the left subtree as the new left child, and the returned node from the right subtree as the new right child of the current node.
4. After the recursive calls, check if the current node's value is 0 and if both its left and right children are null (meaning this subtree doesn't contain a 1). If so, return null to eliminate this part of the tree.
5. If the current node’s value is 1 or it has a non-null child, return the current node to keep it in the tree as part of a valid subtree.

By following these steps, the original binary tree is transformed into a pruned tree where all subtrees not containing a 1 have been successfully removed.