<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) {
        if(preorder.size()==0) return NULL;
        TreeNode* root = new TreeNode(preorder[0]);
        if(preorder.size()==1) return root;
        vector<int> leftInOrder;
        for(int i=0;i<inorder.size();i++){
            if(inorder[i]==preorder[0]){
                //this is the root index
                //left tree -> [0, i-1]
                //right tree -> [i+1, inorder.size()-1]
                vector<int> rightInOrder(inorder.begin()+i+1, inorder.end());
                vector<int> leftPreOrder(preorder.begin()+1, preorder.begin()+1+leftInOrder.size());
                vector<int> rightPreOrder(preorder.begin()+1+leftInOrder.size(), preorder.end());
                root->left = buildTree(leftPreOrder, leftInOrder);
                root->right = buildTree(rightPreOrder, rightInOrder);
                break;
            }else{
                leftInOrder.push_back(inorder[i]);
            }
        }
        return root;
    }
};

//[3 9 20 15 7] [9 3 15 20 7]
//[9] [9]        [20 15 7] [15 20 7]
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