<p>You are given the <code>root</code> of a binary tree.</p>

<p>A ZigZag path for a binary tree is defined as follow:</p>

<ul>
	<li>Choose <strong>any </strong>node in the binary tree and a direction (right or left).</li>
	<li>If the current direction is right, move to the right child of the current node; otherwise, move to the left child.</li>
	<li>Change the direction from right to left or from left to right.</li>
	<li>Repeat the second and third steps until you can&#39;t move in the tree.</li>
</ul>

<p>Zigzag length is defined as the number of nodes visited - 1. (A single node has a length of 0).</p>

<p>Return <em>the longest <strong>ZigZag</strong> path contained in that tree</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/01/22/sample_1_1702.png" style="width: 221px; height: 383px;" />
<pre>
<strong>Input:</strong> root = [1,null,1,1,1,null,null,1,1,null,1,null,null,null,1]
<strong>Output:</strong> 3
<strong>Explanation:</strong> Longest ZigZag path in blue nodes (right -&gt; left -&gt; right).
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/01/22/sample_2_1702.png" style="width: 157px; height: 329px;" />
<pre>
<strong>Input:</strong> root = [1,1,1,null,1,null,null,1,1,null,1]
<strong>Output:</strong> 4
<strong>Explanation:</strong> Longest ZigZag path in blue nodes (left -&gt; right -&gt; left -&gt; right).
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> root = [1]
<strong>Output:</strong> 0
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 5 * 10<sup>4</sup>]</code>.</li>
	<li><code>1 &lt;= Node.val &lt;= 100</code></li>
</ul>

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
from collections import deque
class Solution:
    def longestZigZag(self, root: Optional[TreeNode]) -> int:
        
        heads = deque([(root, "right"),(root, "left")])
        max_length = 0
        visited = set()
        while len(heads) != 0:

            head, direction = heads.popleft()
            curr = head
            length = 0

            while curr.left != None or curr.right != None:
                
                if direction == "left":
                    
                    if curr.right != None:
                        if curr not in visited:
                            heads.append((curr, "right"))
                    visited.add(curr)
                    if curr.left != None:

                        curr = curr.left
                        direction = "right"
                        length += 1
                    else:
                        break

                else:
                    if curr.left != None:
                        if curr not in visited:
                            heads.append((curr, "left"))
                    visited.add(curr)
                    if curr.right != None:

                        curr = curr.right
                        direction = "left"
                        length += 1
                    else:
                        break
            
            if length > max_length:
                max_length = length
        return max_length

28000