Approach

To tackle the problem of finding the longest univalue path in a binary tree, we can follow a structured approach:

1. Understanding the Problem:

• A univalue path is a path where all nodes have the same value.

• The longest univalue path can be defined as the maximum length of such paths that can be formed from the root to any of its descendants.

• Tree Traversal:

• We will utilize Depth-First Search (DFS) for traversing the tree nodes effectively.

• Recursive Function:

• Create a recursive function that returns the length of the longest univalue path starting from the current node.

• Path Calculation:

• At each node, check its left and right children to see if they have the same value as the current node. If they do, extend the path length accordingly.

• Global Variable:

• Use a global variable to keep track of the maximum path length found during the traversal.

Key Points

• Node Comparison: Essential to compare the current node with its children to determine if they can extend the univalue path.

• Path Length Calculation: The path length is calculated as the number of edges, not the number of nodes.

• DFS Utilization: Leveraging DFS allows us to explore all potential paths in an efficient manner.

Standard Response

class TreeNode:
 def __init__(self, val=0, left=None, right=None):
 self.val = val
 self.left = left
 self.right = right

class Solution:
 def longestUnivaluePath(self, root: TreeNode) -> int:
 self.max_length = 0

 def dfs(node):
 if not node:
 return 0

 left_length = dfs(node.left)
 right_length = dfs(node.right)

 # Lengths for univalue paths
 left_univalue = left_length + 1 if node.left and node.left.val == node.val else 0
 right_univalue = right_length + 1 if node.right and node.right.val == node.val else 0

 # Update the maximum length found
 self.max_length = max(self.max_length, left_univalue + right_univalue)

 # Return the length of the longest univalue path that can be extended to the parent
 return max(left_univalue, right_univalue)

 dfs(root)
 return self.max_length

Tips & Variations

Common Mistakes to Avoid

• Ignoring Leaf Nodes: Make sure to handle leaf nodes correctly; they contribute a path of length 0 when calculating.

• Not Returning Lengths: Ensure that the recursive function returns lengths correctly, as it impacts the overall path length.

Alternative Ways to Answer

• Iterative Approach: Instead of recursion, one could use an iterative approach with a stack to traverse the tree. However, this is less common for tree problems.

• Using BFS: Although less efficient for this particular problem, breadth-first search can also be adapted but is generally not optimal for depth-related calculations.

Role-Specific Variations

• For Technical Roles: Emphasize optimization and edge cases, such as handling trees with all identical values or handling null nodes.

• For Managerial Roles: Focus on the algorithm's efficiency and how you would communicate this solution to a team or non-technical stakeholders.

Follow-Up Questions

• How would you handle edge cases, such as an empty tree or a tree where all values are the same?

• Can you explain the time and space complexity of your solution?

• What would you change in your approach if you were required to find the longest path with a specific value instead of a univalue path?