/**
 * 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:
    //f[i]，选第i个点能获得的最大价值
    //g[i]，不选第i个点能获得的最大价值
    unordered_map<TreeNode*, int> f, g;
    void dfs(TreeNode* u){
        if(!u)return ;
        dfs(u->left);
        dfs(u->right);
        f[u] = u->val+g[u->left]+g[u->right];
        g[u] = max(f[u->left],g[u->left])+max(f[u->right],g[u->right]);
    }
    int rob(TreeNode* root) {
        dfs(root);
        return max(f[root], g[root]);
    }
};