<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.
//  * struct TreeNode {
//  *     int val;
//  *     TreeNode *left;
//  *     TreeNode *right;
//  *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
//  *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
//  *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
//  * };
//  */
// class Solution {
// public:
//     void findpath(TreeNode* root,bool isRight,int& ct){
//         if(root==NULL){
//             return;
//         }      
//         if(isRight){
//             ct++;
//             findpath(root->right,false,ct);
//         }
//         else{
//             ct++;
//             findpath(root->left,true,ct); 
//         }
//     }

//     void preorder(TreeNode* root,vector<TreeNode*>&ans){
//         if(root==NULL){
//             return;
//         }
//         ans.push_back(root);
//         preorder(root->left,ans);
//         preorder(root->right,ans);
//     }

//     int longestZigZag(TreeNode* root) {

//         vector<TreeNode*>ans;
//         preorder(root,ans);
//         int maxi=0;
//         for(auto it:ans){
//             int ct1=0,ct2=0;
//             findpath(it,true,ct1);
//             findpath(it,false,ct2);
//             int curr_max=max(ct1-1,ct2-1);
//             maxi=max(maxi,curr_max);
//         }
//         return maxi;
//     }
// };

class Solution {
public:
    void findpath(TreeNode* root, bool isRight, int& ct) {
        if (root == nullptr) return;

        ct++;
        if (isRight) {
            if (root->right) findpath(root->right, false, ct);
        } else {
            if (root->left) findpath(root->left, true, ct);
        }
    }

    void preorder(TreeNode* root, vector<TreeNode*>& ans) {
        if (root == nullptr) return;
        ans.push_back(root);
        preorder(root->left, ans);
        preorder(root->right, ans);
    }

    int longestZigZag(TreeNode* root) {
        vector<TreeNode*> ans;
        preorder(root, ans);
        int maxi = 0;

        for (auto it : ans) {
            int ct1 = 0, ct2 = 0;
            findpath(it, true, ct1);
            findpath(it, false, ct2);

            int curr_max = max(ct1 - 1, ct2 - 1);
            maxi = max(maxi, curr_max);
        }

        return maxi;
    }
};

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