<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>

auto init = []() {cin.tie(0); ios::sync_with_stdio(0); return 1;}();
class Solution {
public:
    int preorderIndex;
    unordered_map<int, int> map;
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        for(int i = 0; i < inorder.size(); i++) {
            map[inorder[i]] = i;
        }
        preorderIndex = 0;
        return build(preorder, 0, inorder.size() - 1);
    }

    TreeNode* build(vector<int> preorder, int s, int e) {
        if(s > e) return NULL;

        int rootVal = preorder[preorderIndex++];
        TreeNode* root = new TreeNode(rootVal);
        int mid = map[rootVal];

        root->left = build(preorder, s, mid - 1);
        root->right = build(preorder, mid + 1, e);

        return root;
    }
};
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