How should I practice All Root-to-Leaf Paths in a Binary Tree?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Google onsite interview problems in FastPrep.

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FastPrep tags this as a Google onsite interview coding practice problem when the problem catalog has that company and stage context.

All Root-to-Leaf Paths in a Binary Tree

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Problem statement

Given the root of a binary tree, return every path from the root to a leaf.

Serialize a path by joining its node values with ->.
Return paths in left-to-right depth-first order: completely visit a node's left subtree before its right subtree.
Return an empty array for an empty tree.

A leaf has no left child and no right child. Do not use global or static mutable state.

Deep-tree follow-up

How can an explicit stack preserve the same traversal and backtracking behavior without risking recursive call-stack overflow?

Function

binaryTreePaths(root: TreeNode) → String[]

Examples

Example 1

root = [1,2,3,null,5]return = ["1->2->5","1->3"]

The left leaf produces 1->2->5, followed by the right leaf path 1->3.

Example 2

root = [1]return = ["1"]

The root is also a leaf, so the only path contains its value.

Example 3

root = []return = []

An empty tree has no root-to-leaf paths.

Example 4

root = [-1,-2,3,null,-4]return = ["-1->-2->-4","-1->3"]

Negative values are preserved in the path strings, and the left path still appears before the right path.

Constraints

The tree contains between 0 and 100000 nodes.
-2^31 <= Node.val <= 2^31 - 1.
The tree may be skewed to a depth of 100000.