Equal Tree Partition
<p>Given the <code>root</code> of a binary tree, return <code>true</code><em> if you can partition the tree into two trees with equal sums of values after removing exactly one edge on the original tree</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0600-0699/0663.Equal%20Tree%20Partition/images/split1-tree.jpg" style="width: 500px; height: 204px;" />
<pre>
<strong>Input:</strong> root = [5,10,10,null,null,2,3]
<strong>Output:</strong> true
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0600-0699/0663.Equal%20Tree%20Partition/images/split2-tree.jpg" style="width: 277px; height: 302px;" />
<pre>
<strong>Input:</strong> root = [1,2,10,null,null,2,20]
<strong>Output:</strong> false
<strong>Explanation:</strong> You cannot split the tree into two trees with equal sums after removing exactly one edge on the tree.
</pre>

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

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 10<sup>4</sup>]</code>.</li>
	<li><code>-10<sup>5</sup> &lt;= Node.val &lt;= 10<sup>5</sup></code></li>
</ul>
Tree; Depth-First Search; Binary Tree
/**
 * 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:
    vector<int> seen;

    bool checkEqualTree(TreeNode* root) {
        int s = sum(root);
        if (s % 2 != 0) return false;
        seen.pop_back();
        return count(seen.begin(), seen.end(), s / 2);
    }

    int sum(TreeNode* root) {
        if (!root) return 0;
        int l = sum(root->left), r = sum(root->right);
        int s = l + r + root->val;
        seen.push_back(s);
        return s;
    }
};