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 <code>1, 5 * 10⁴</code>.

• 1 <= Node.val <= 100