Path Sum - Solution & Explanation

This approach uses a recursive DFS strategy to navigate from the root to each leaf, calculating the cumulative sum along the path. If we find a path where the cumulative sum equals the targetSum at a leaf node, we return true. Otherwise, we continue exploring other paths. In case we exhaust all paths without finding a valid path, we return false.

In this Python solution, we define a recursive function hasPathSum that deducts the current node's value from targetSum as we traverse the tree. If we reach a leaf node (both children are None) and the remaining targetSum equals the leaf node's value, we return true; otherwise, false. The recursion continues for left and right subtrees.

In contrast to the recursive method, this approach utilizes an explicit stack to iteratively perform DFS, tracking the cumulative sum along each path. Nodes are pushed onto the stack with their cumulative sums traversed thus far, effectively replacing the recursion stack with an explicit stack to manage state manually. This can help in environments with limited recursion support.

The Python solution leverages a stack to simulate DFS. When visiting a node, the accumulated sum of the path is tracked, ensuring each leaf node is evaluated against targetSum. Left and right children are pushed onto the stack with updated path sums.