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程式語言 - LeetCode - C++ - 508. Most Frequent Subtree Sum

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題目：


解答：

/**
 * 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> findFrequentTreeSum(TreeNode* root) {
        int mx = 0;
        unordered_map<int, int> mp;

        auto dfs = [&](this auto&& dfs, TreeNode *n) -> int {
            if (!n) {
                return 0;
            }

            int l = dfs(n->left);
            int r = dfs(n->right);
            int v = n->val + l + r;

            mp[v] += 1;
            mx = max(mx, mp[v]);

            return v;
        };

        dfs(root);

        vector<int> ans;
        for (auto [k, v] : mp) {
            if (mx == v) {
                ans.push_back(k);
            }
        }

        return ans;
    }
};