class Solution {
public:
    int rob(TreeNode* root) {
        return solveRob(root, true);
    }
private:
    int solveRob(TreeNode* node, bool can_rob) {
        if (!node) return 0;

        int do_not_rob_res = solveRob(node->left, true) + solveRob(node->right, true);
        int rob_res = 0;
        if (can_rob)
            rob_res = node->val + solveRob(node->left, false) + solveRob(node->right, false);

        return max(do_not_rob_res, rob_res);
    }
};