<p>Given the <code>root</code> of a binary tree, return the most frequent <strong>subtree sum</strong>. If there is a tie, return all the values with the highest frequency in any order.</p>

<p>The <strong>subtree sum</strong> of a node is defined as the sum of all the node values formed by the subtree rooted at that node (including the node itself).</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/04/24/freq1-tree.jpg" style="width: 207px; height: 183px;" />
<pre>
<strong>Input:</strong> root = [5,2,-3]
<strong>Output:</strong> [2,-3,4]
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/04/24/freq2-tree.jpg" style="width: 207px; height: 183px;" />
<pre>
<strong>Input:</strong> root = [5,2,-5]
<strong>Output:</strong> [2]
</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>

/**
 * 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 {
private:
    int calculate(TreeNode* root, vector<int>& treeSum) {
        if(root == NULL) return 0;
        int left = calculate(root->left, treeSum);
        int right = calculate(root->right, treeSum);
        int result = left + right + root->val;
        treeSum.push_back(result);
        return result;
    }
public:
    vector<int> findFrequentTreeSum(TreeNode* root) {
        vector<int> treeSum;
        calculate(root, treeSum);
        sort(treeSum.begin(), treeSum.end());
        int ct = 1;
        int maxCt = ct;
        int size = treeSum.size();
        for(int i=1;i<size;i++) {
            if(treeSum[i] == treeSum[i-1]) {
                ct++;
            } else {
                maxCt = max(maxCt, ct);
                ct = 1;
            }
        }
        maxCt = max(maxCt, ct);
        ct = 1;
        vector<int> result;
        if(ct == maxCt) result.push_back(treeSum[0]);
        for(int i=1;i<size;i++) {
            if(treeSum[i] == treeSum[i-1]) {
                ct++;
            } else ct = 1;
            if(ct == maxCt) {
                if(result.size() > 0 && result[result.size()-1] == treeSum[i]) continue;
                result.push_back(treeSum[i]);
            }
        }
        return result;
    }
};
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