<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>

/**
 * 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:
    Solution(){
        ios_base::sync_with_stdio(0);
        cin.tie(0);
        cout.tie(0);
    }
    TreeNode* buildTree(vector<int> inorder, vector<int> postorder) {
        int root_val = -3001;
        int root_idx = -1;
        int n = inorder.size();
        if (n == 0) return 0;

        for (int i=0; i<n; i++){
            if (postorder[n-1] == inorder[i]){
                root_val = inorder[i];
                root_idx = i;
            }
        }
        TreeNode* root = new TreeNode(root_val);

        // vector<int> tmp (postorder.begin()+root_idx, postorder.end()-1);
        // cout << tmp.size() << endl;
        // for (int i: tmp){
        //     cout << i << endl;
        // }
        // cout <<"=========" << endl;

        root->left = (n==1)? 0: buildTree(vector<int>(inorder.begin(), inorder.begin()+root_idx), vector<int>(postorder.begin(), postorder.begin()+root_idx));
        root->right = (n==1)? 0: buildTree(vector<int>(inorder.begin()+1+root_idx, inorder.end()), vector<int>(postorder.begin()+root_idx, postorder.end()-1));

        return root;
        
    }
};
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