Solution.cpp

/**
 * 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:
    double maximumAverageSubtree(TreeNode* root) {
        double ans = 0;
        auto dfs = [&](this auto&& dfs, TreeNode* root) -> pair<int, int> {
            if (!root) {
                return {0, 0};
            }
            auto [ls, ln] = dfs(root->left);
            auto [rs, rn] = dfs(root->right);
            int s = root->val + ls + rs;
            int n = 1 + ln + rn;
            ans = max(ans, s * 1.0 / n);
            return {s, n};
        };
        dfs(root);
        return ans;
    }
};