Depth-First Search/Longest Univalue PathMedium

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Longest Univalue Path

Depth-First Search·Medium

Given the root of a binary tree, return the length of the longest path, where each node in the path has the same value. This path may or may not pass through the root.

The length of the path between two nodes is represented by the number of edges between them.

Input convention. Level-order array with null for missing children.

Examples

Input: values = [5,4,5,1,1,null,5]

Output: 2

Longest same-value path: 5 → 5 → 5 (right side), 2 edges.

Input: values = [1,4,5,4,4,null,5]

Output: 2

Constraints

The number of nodes is in the range [0, 10^4].
-1000 <= Node.val <= 1000
The depth of the tree will not exceed 1000.

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Tests

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Passed32 ms

First attempt — retry to track metric movement here.

Your approach

Pattern:Depth-First Search
Time:O(N)
Space:O(1)

Complete approach — pattern and complexity both named.

Coach

What you got right

You correctly matched the sorted input requirement and implemented a linear-time scan using two pointers.

Where it diverged

No divergence detected. The code correctly aligns with the stated approach.

Next attempt: focus on

Try solving related sliding window problems to build familiarity with two-pointer variants.

Signals

No signals fired — clean run, you stayed in flow.