为什么用动态数组洛谷就要报错 报错如下：``` /tmp/compiler_8o22mj8o/src: In function ‘void dfs(int, int)’: /tmp/compiler_8o22mj8o/src:6:17: 错误：对成员‘size’的请求出现在‘e.std::vector::operator’中，而后者具有非类类型‘int’ 6 | if(e[u].size()){ | ^~~~ /tmp/compiler_8o22mj8o/src:7:35: 警告：range-based ‘for’ loops only available with ‘-std=c++11’ or ‘-std=gnu++11’ [-Wc++11-extensions] 7 | for(const int v : e[u]){ | ^ /tmp/compiler_8o22mj8o/src:7:38: 错误：生成指向引用类型‘int&’的引用 7 | for(const int v : e[u]){ | ^ /tmp/compiler_8o22mj8o/src: In function ‘void bfs()’: /tmp/compiler_8o22mj8o/src:22:35: 警告：range-based ‘for’ loops only available with ‘-std=c++11’ or ‘-std=gnu++11’ [-Wc++11-extensions] 22 | for(const int v : e[u]){ | ^ /tmp/compiler_8o22mj8o/src:22:38: 错误：生成指向引用类型‘int&’的引用 22 | for(const int v : e[u]){ | ^ /tmp/compiler_8o22mj8o/src:31:35: 警告：range-based ‘for’ loops only available with ‘-std=c++11’ or ‘-std=gnu++11’ [-Wc++11-extensions] 31 | for(const int v : e[u]){ | ^ /tmp/compiler_8o22mj8o/src:31:38: 错误：生成指向引用类型‘int&’的引用 31 | for(const int v : e[u]){ | ^ /tmp/compiler_8o22mj8o/src: In function ‘int main()’: /tmp/compiler_8o22mj8o/src:44:22: 错误：对成员‘push_back’的请求出现在‘e.std::vector::operator’中，而后者具有非类类型‘int’ 44 | e[x].push_back(y); | ^~~~~~~~~ /tmp/compiler_8o22mj8o/src:45:22: 错误：对成员‘push_back’的请求出现在‘e.std::vector::operator’中，而后者具有非类类型‘int’ 45 | e[y].push_back(x); | ^~~~~~~~~