public class Solution
extends Object
1372 - Longest ZigZag Path in a Binary Tree\.
Medium
You are given the `root` of a binary tree.
A ZigZag path for a binary tree is defined as follow:
* Choose **any** node in the binary tree and a direction (right or left).
* If the current direction is right, move to the right child of the current node; otherwise, move to the left child.
* Change the direction from right to left or from left to right.
* Repeat the second and third steps until you can't move in the tree.
Zigzag length is defined as the number of nodes visited - 1. (A single node has a length of 0).
Return _the longest **ZigZag** path contained in that tree_.
**Example 1:**
**Input:** root = [1,null,1,1,1,null,null,1,1,null,1,null,null,null,1,null,1]
**Output:** 3
**Explanation:** Longest ZigZag path in blue nodes (right -> left -> right).
**Example 2:**
**Input:** root = [1,1,1,null,1,null,null,1,1,null,1]
**Output:** 4
**Explanation:** Longest ZigZag path in blue nodes (left -> right -> left -> right).
**Example 3:**
**Input:** root = [1]
**Output:** 0
**Constraints:**
* The number of nodes in the tree is in the range [1, 5 * 104].
* `1 <= Node.val <= 100`