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Binary Tree Tilt

Depth-First Search·Easy

Given the root of a binary tree, return the sum of every node's tilt.

The tilt of a tree node is the absolute difference between the sum of all left subtree node values and the sum of all right subtree node values. If a node does not have a left child, then the sum of the left subtree node values is treated as 0. The same applies for the right child.

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

Examples

Input: values = [1,2,3]

Output: 1

Tilt of 2 = 0, tilt of 3 = 0, tilt of 1 = |2 - 3| = 1. Sum = 1.

Input: values = [4,2,9,3,5,null,7]

Output: 15

Constraints

The number of nodes is in the range [0, 10^4].
-1000 <= Node.val <= 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.