Step-By-Step Directions From a Binary Tree Node to Another Python/Java solution

Python and Java solutions typically implement DFS to build paths or parent maps. After identifying the lowest common ancestor or exploring neighbors, the algorithm constructs the direction string using 'L', 'R', and 'U'. Both implementations run in O(n) time and use O(n) auxiliary space.

What is the best approach for Step-By-Step Directions From a Binary Tree Node to Another?

The most common approach finds the path from the root to both nodes using DFS, then identifies the lowest common ancestor by comparing the two paths. Replace the remaining steps in the start path with 'U' and append the remaining moves from the destination path. This runs in O(n) time and O(n) space and is typically expected in coding interviews.

Is Step-By-Step Directions From a Binary Tree Node to Another asked at Google/Amazon/Meta?

Binary tree path and lowest common ancestor style problems frequently appear in interviews at companies like Google, Amazon, and Meta. Variants of this problem test DFS traversal, tree path construction, and reasoning about ancestor relationships.

What data structure is used in Step-By-Step Directions From a Binary Tree Node to Another?

The solution primarily uses binary tree traversal with recursion or an explicit stack. Some implementations also maintain arrays for root-to-node paths or a hash map that stores each node's parent to allow upward traversal in the tree.

What is the time complexity of Step-By-Step Directions From a Binary Tree Node to Another?

The optimal solutions run in O(n) time where n is the number of nodes in the binary tree. Each node is visited at most once during DFS traversal. Space complexity is O(n) due to recursion stack, path storage, or the parent map used during traversal.

Description Hints 3 Solution Video 16:50

2096. Step-By-Step Directions From a Binary Tree Node to Another

Q: Is Step-By-Step Directions From a Binary Tree Node to Another easy or hard?

This problem is classified as Medium difficulty. The challenge comes from recognizing that the path between two nodes goes through their lowest common ancestor and translating that relationship into direction characters.

Q: How to solve Step-By-Step Directions From a Binary Tree Node to Another in O(n)?

Run a depth-first search from the root to record paths to both the start node and destination node. Compare the paths to find the first position where they differ, which represents the lowest common ancestor. Convert the remaining start path to 'U' moves and append the remaining destination path moves to build the final direction string.

Medium56.3% acceptance6 companies

You are given the root of a binary tree with n nodes. Each node is uniquely assigned a value from 1 to n. You are also given an integer startValue representing the value of the start node s, and a different integer destValue representing the value of the destination node t.

Find the shortest path starting from node s and ending at node t. Generate step-by-step directions of such path as a string consisting of only the uppercase letters 'L', 'R', and 'U'. Each letter indicates a specific direction:

'L' means to go from a node to its left child node.
'R' means to go from a node to its right child node.
'U' means to go from a node to its parent node.

Return the step-by-step directions of the shortest path from node s to node t.

Example 1:

Input: root = [5,1,2,3,null,6,4], startValue = 3, destValue = 6
Output: "UURL"
Explanation: The shortest path is: 3 → 1 → 5 → 2 → 6.

Example 2:

Input: root = [2,1], startValue = 2, destValue = 1
Output: "L"
Explanation: The shortest path is: 2 → 1.

Constraints:

The number of nodes in the tree is n.
2 <= n <= 10⁵
1 <= Node.val <= n
All the values in the tree are unique.
1 <= startValue, destValue <= n
startValue != destValue

Asked at 6 companies

Snowflake Databricks Tiktok

Google Amazon Meta

Topics

Hints open one at a time

Hint 1

The shortest path between any two nodes in a tree must pass through their Lowest Common Ancestor (LCA). The path will travel upwards from node s to the LCA and then downwards from the LCA to node t.

Hint 2

Find the path strings from root → s, and root → t. Can you use these two strings to prepare the final answer?

Hint 3

Remove the longest common prefix of the two path strings to get the path LCA → s, and LCA → t. Each step in the path of LCA → s should be reversed as 'U'.

16:50

Still stuck?Read 4 approaches, or watch a walkthrough.

Open solution