<p>Given two integer arrays <code>inorder</code> and <code>postorder</code> where <code>inorder</code> is the inorder traversal of a binary tree and <code>postorder</code> is the postorder 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> inorder = [9,3,15,20,7], postorder = [9,15,7,20,3]
<strong>Output:</strong> [3,9,20,null,null,15,7]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> inorder = [-1], postorder = [-1]
<strong>Output:</strong> [-1]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= inorder.length &lt;= 3000</code></li>
	<li><code>postorder.length == inorder.length</code></li>
	<li><code>-3000 &lt;= inorder[i], postorder[i] &lt;= 3000</code></li>
	<li><code>inorder</code> and <code>postorder</code> consist of <strong>unique</strong> values.</li>
	<li>Each value of <code>postorder</code> also appears in <code>inorder</code>.</li>
	<li><code>inorder</code> is <strong>guaranteed</strong> to be the inorder traversal of the tree.</li>
	<li><code>postorder</code> is <strong>guaranteed</strong> to be the postorder traversal of the tree.</li>
</ul>

class Solution {
public:

    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
        if (postorder.empty()) {
            return nullptr;
        }

        int root_val = postorder.back(); // Root is the last element in postorder
        TreeNode* newTree = new TreeNode(root_val);

        if (postorder.size() == 1) {
            return newTree;
        }

        vector<int> inorder1;
        int i = 0;

        // Find the index of the root in inorder traversal
        while (inorder[i] != root_val) {
            inorder1.push_back(inorder[i]);
            i++;
        }

        vector<int> inorder2(inorder.begin() + i + 1, inorder.end());
        postorder.pop_back(); // Remove the root from postorder

        if (!inorder2.empty()) {
            vector<int> postorder2(postorder.end() - inorder2.size(), postorder.end());
            newTree->right = buildTree(inorder2, postorder2);
            postorder.erase(postorder.end() - inorder2.size(), postorder.end());
        }

        if (!inorder1.empty()) {
            newTree->left = buildTree(inorder1, postorder);
        }

        return newTree;
    }
};

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