<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>

class Solution {
public:
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        if (preorder.empty() || inorder.empty()) return nullptr;

        queue<TreeNode*> q;
        unordered_map<int, vector<int>> mp;
        TreeNode *root = new TreeNode(preorder[0]);
        q.push(root);
        mp[root->val] = inorder;

        while (!q.empty()) {
            TreeNode* current = q.front();
            q.pop();
            
            int val = current->val;
            auto it = find(mp[val].begin(), mp[val].end(), val);

            vector<int> left(mp[val].begin(), it);
            vector<int> right(it + 1, mp[val].end());

            it = find(preorder.begin(), preorder.end(), val);
            bool isleft = false;
            if (!left.empty()) {
                it++;
                TreeNode *ln = new TreeNode(*it);
                current->left = ln;
                mp[*it] = left;
                q.push(ln);
                isleft = !isleft;
            }
            if (!right.empty()) {
                it = (isleft) ? (it + left.size()) : (it + 1);
                TreeNode *rn = new TreeNode(*it);
                current->right = rn;
                mp[*it] = right;
                q.push(rn);
            }
        }
        return root;
    }
};

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