<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 {
private:
    // TreeNode* helper(int preStart, int inStart, int inEnd, vector<int>& pre, vector<int>& in) {
    //     if (preStart > pre.size()-1 || inStart > inEnd) return nullptr;
    //     TreeNode *node = new TreeNode(pre[preStart]);
    //     if (inEnd == inStart) return node;
    //     int idx = 0;
    //     for (int i = inStart; i <= inEnd; i++) {
    //         if (in[i] == pre[preStart]) {
    //             idx = i;
    //             break;
    //         }
    //     }
    //     node->left = helper(preStart+1, inStart, idx-1, pre, in);
    //     node->right = helper(preStart+idx-inStart+1, idx+1, inEnd, pre, in);
    //     return node;
    // }
public:
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        // return helper(0, 0,inorder.size()-1, preorder, inorder);
        
        if (!inorder.empty()) {
            int idx = inorder.size()-1;
            for (int i = 0; i < inorder.size(); i++) {
                if (inorder[i] == preorder[0]) {
                    idx = i;
                    break;
                }
            }
            
            TreeNode *root = new TreeNode(preorder[0]);
            preorder.erase(preorder.begin());
            vector<int> split;
            if (idx > 0) {
                split = vector(inorder.begin(), inorder.begin()+idx);
                root->left = buildTree(preorder, split);
            }
            if (idx < inorder.size() - 1) {
                split = vector(inorder.begin()+idx+1, inorder.end());
                root->right = buildTree(preorder, split);
            }
            return root;
        }
        return NULL;


        //  if (!inorder.empty()) {
        //     int ind = find(inorder.begin(), inorder.end(), preorder[0]) - inorder.begin();
        //     TreeNode* root = new TreeNode(preorder[0]);
        //     preorder.erase(preorder.begin());
        //     vector<int> leftInorder(inorder.begin(), inorder.begin() + ind);
        //     vector<int> rightInorder(inorder.begin() + ind + 1, inorder.end());
        //     root->left = buildTree(preorder, leftInorder);
        //     root->right = buildTree(preorder, rightInorder);
        //     return root;
        // }
        // return nullptr;
    }
};
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