<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:
    int findPos(vector<int> v, int target) {
        int l = 0, r = v.size()-1;

        for(auto i=0; i<v.size(); i++) {
            if(v[i] == target)     return i;
        }

        return -1;
    }

    TreeNode* build(vector<int>& pre, vector<int>& in, TreeNode* node) {
        
        node->val = pre[0];
        if(pre.size() == 1)    return node;

        int pos = findPos(in, pre[0]);

        if(pos != 0) {
            TreeNode* left = new TreeNode();
            vector<int> pre_l = {pre.begin()+1, pre.begin()+pos+1};
            vector<int> pre_r = {in.begin(), in.begin()+pos};
            left = build(pre_l, pre_r, left);
            node->left = left;
        }

        if(pos != in.size()-1) {
            TreeNode* right = new TreeNode();        
            vector<int> in_l = {pre.begin()+pos+1, pre.end()};
            vector<int> in_r = {in.begin()+pos+1, in.end()};
            right = build(in_l, in_r, right);
            node->right = right;
        }
        
        return node;
    }
public:
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {

        if(!preorder.size()) {
            return NULL;
        }
        
        TreeNode* root = new TreeNode();
        build(preorder, inorder, root);

        return root;
    }
};
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