<p>Given two integer arrays <code>preorder</code> and <code>inorder</code> where <code>preorder</code> is the preorder traversal of a binary tree and <code>inorder</code> is the inorder traversal of the same tree, construct and return <em>the binary tree</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/19/tree.jpg" style="width: 277px; height: 302px;" />
<pre>
<strong>Input:</strong> preorder = [3,9,20,15,7], inorder = [9,3,15,20,7]
<strong>Output:</strong> [3,9,20,null,null,15,7]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> preorder = [-1], inorder = [-1]
<strong>Output:</strong> [-1]
</pre>

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

<ul>
	<li><code>1 &lt;= preorder.length &lt;= 3000</code></li>
	<li><code>inorder.length == preorder.length</code></li>
	<li><code>-3000 &lt;= preorder[i], inorder[i] &lt;= 3000</code></li>
	<li><code>preorder</code> and <code>inorder</code> consist of <strong>unique</strong> values.</li>
	<li>Each value of <code>inorder</code> also appears in <code>preorder</code>.</li>
	<li><code>preorder</code> is <strong>guaranteed</strong> to be the preorder traversal of the tree.</li>
	<li><code>inorder</code> is <strong>guaranteed</strong> to be the inorder traversal of the tree.</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:
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        int index = 0;
        return build(index, preorder, inorder);

    }

    TreeNode *build(int &preorderIndex, vector<int> &preorder, vector<int> &inorder)
    {
        if (inorder.size() == 0)
        {
            return nullptr;
        }

        vector<int> left_array = {};
        vector<int> right_array = {};
        
        int val = preorder[preorderIndex++];

        TreeNode *root = new TreeNode(val);
        splitTree(val, inorder, left_array, right_array);

        root->left = build(preorderIndex, preorder, left_array);
        root->right = build(preorderIndex, preorder, right_array);

        return root;
    }

    void splitTree(int root, const vector<int> &inorder, vector<int> &left, vector<int> &right)
    {
        bool root_found = false;
        for (int i=0; i < inorder.size(); i++)
        {
            if (inorder[i] == root)
            {
                root_found = true;
                continue;
            }

            if (root_found)
            {
                right.push_back(inorder[i]);
            }
            else
            {
                left.push_back(inorder[i]);
            }
        }
    }
};
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