Method addOneRow

Trees/addOneRowToTree.cpp:133–141

        return;
    }
    TreeNode* addOneRow(TreeNode* root, int val, int depth) {
        if(depth==1){
            TreeNode *temp=new TreeNode(val);
            temp->left=root;
            return temp;
        }
        dfs(root,val,depth,1);
        return root;
    }
};