leetcode 965. univalued binary tree（树）

class  {
private:
    int univalue;
    
    bool dfs(TreeNode* root) {
        if (root == NULL) return true;
        if (root->val != univalue)
            return false;
        return dfs(root->left) && dfs(root->right);
    }
    
public:
    bool isUnivalTree(TreeNode* root) {
        univalue = root->val;
        return dfs(root);
    }
};