<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>

/*
 * start at end of postorder o/w same?
 *
 */

/**
 * 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:
    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
        TreeNode* root = build(postorder, inorder);

        return root;
    }

    TreeNode* build(vector<int>& post_o, vector<int>& in_o) {
        if ((0 == in_o.size()) || (0 == post_o.size())) {
            return NULL;
        }
        TreeNode* node = new TreeNode();
        if (1 == post_o.size()) {
            node->val = post_o[0];
            return node;
        }

        int curr = post_o[post_o.size()-1];
        ptrdiff_t in_idx = distance(in_o.begin(), find(in_o.begin(), in_o.end(), curr));
        vector<int> in_left = {in_o.begin(), in_o.begin()+in_idx};
        int left_len = in_left.size();
        vector<int> in_right = {in_o.begin()+(in_idx+1), in_o.end()};
        int right_len = in_right.size();

        node->val = curr;
        vector<int> left_in = {in_o.begin(), in_o.begin()+in_idx};
        vector<int> left_post = {post_o.begin(), post_o.begin()+left_len};
        node->left = build(left_post, left_in);
        vector<int> right_in = {in_o.begin()+(in_idx+1), in_o.end()};
        vector<int> right_post = {post_o.begin()+left_len, post_o.begin()+(left_len+right_len)};
        node->right = build(right_post, right_in);

        return node;
    }
};
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