Binary Tree Pruning - Solution & Explanation

This approach uses post-order traversal to traverse each subtree and decide if it should be pruned. Starting from the leaf nodes, it recursively checks if a subtree contains a 1. If a subtree doesn't contain any 1s, it returns null. This way, when the recursion unwinds, only relevant subtrees are kept.

The provided C code represents a function that conducts a post-order traversal starting from the given root node. It uses recursion to visit each node, first addressing the left and right subtrees. If a node's value is 0 and both its subtrees are NULL, the node is pruned by freeing its memory and returning NULL. Otherwise, the node is returned intact. The traversal ensures all subtrees without a 1 are effectively pruned away.

By utilizing an iterative traversal using a stack, the tree can be pruned without recursion. This approach mimics the recursion stack by using an explicit stack to manage nodes that need to be processed. Once the subtree rooted at a node is evaluated, decisions are made to prune or retain nodes based on whether a 1 is found.

The C implementation employs a boolean helper function, containsOne, which verifies if any subtree contains the value 1. The iterative sense is simulated by the helper function instead of explicit stack management. Nodes without 1 in their subtrees are trimmed, promoting a structured pruning process.