题目：

题解：

struct SubtreeStatus {
    int selected;
    int notSelected;
};

struct SubtreeStatus dfs(struct TreeNode *node) {
    if (!node) {
        return (struct SubtreeStatus){0, 0};
    }
    struct SubtreeStatus l = dfs(node->left);
    struct SubtreeStatus r = dfs(node->right);
    int selected = node->val + l.notSelected + r.notSelected;
    int notSelected = fmax(l.selected, l.notSelected) + fmax(r.selected, r.notSelected);
    return (struct SubtreeStatus){selected, notSelected};
}

int rob(struct TreeNode *root) {
    struct SubtreeStatus rootStatus = dfs(root);
    return fmax(rootStatus.selected, rootStatus.notSelected);
}