<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.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def helper(self, val, val_arr):
        idx = val_arr.index(val)
        left_vals = val_arr[:idx]
        right_vals = val_arr[idx+1:] if idx+1 < len(val_arr) else []
        return left_vals, right_vals
        
        
    def buildTree(self, preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
        
        stack=[]
        hashmap={}
        val = preorder.pop(0)
        root = TreeNode(val)
        stack.append(root)
        left_vals, right_vals = self.helper(val, inorder)
        hashmap[val]=[left_vals, right_vals]
        iter = root
        while preorder:
            
            val = preorder.pop(0)
            print(iter.val, "val of iter")
            print(val, "val")
            left_vals = hashmap[iter.val][0]
            right_vals = hashmap[iter.val][1]
            
            if val in left_vals:
                iter.left = TreeNode(val)
                left_vals_, right_vals_ = self.helper(val, left_vals)
                iter = iter.left
                hashmap[val] = [left_vals_, right_vals_]
                stack.append(iter)
                # print("iter in left", iter)
            elif val in right_vals:
                iter.right = TreeNode(val)
                left_vals_, right_vals_ = self.helper(val, right_vals)
                iter = iter.right
                hashmap[val] = [left_vals_, right_vals_]
                stack.append(iter)
                # print("iter in right", iter)
            else:
                iter = stack.pop()
                preorder.insert(0, val)
                # print(iter, "iter in else")
        return root
        
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