answer.code:11:52: error: ‘int link [2000010]’ redeclared as different kind of entity
   11 | int tot_edge, head[maxn], to[maxn<<1], link[maxn<<1];
      |                                                    ^
In file included from /usr/include/c++/13/bits/atomic_wait.h:44,
                 from /usr/include/c++/13/bits/atomic_base.h:42,
                 from /usr/include/c++/13/bits/shared_ptr_atomic.h:33,
                 from /usr/include/c++/13/memory:81,
                 from /usr/include/x86_64-linux-gnu/c++/13/bits/stdc++.h:56,
                 from answer.code:1:
/usr/include/unistd.h:789:12: note: previous declaration ‘int link(const char*, const char*)’
  789 | extern int link (const char *__from, const char *__to)
      |            ^~~~
answer.code: In function ‘void add_edge(int, int)’:
answer.code:14:16: warning: pointer to a function used in arithmetic [-Wpointer-arith]
   14 |   link[tot_edge] = head[x];
      |                ^
answer.code:14:18: error: assignment of read-only location ‘*(link + ((sizetype)tot_edge))’
   14 |   link[tot_edge] = head[x];
      |   ~~~~~~~~~~~~~~~^~~~~~~~~
answer.code: In function ‘pii dfs(int, int, int)’:
answer.code:21:41: warning: pointer to a function used in arithmetic [-Wpointer-arith]
   21 |   for(int now=head[x]; now; now=link[now]) {
      |                                         ^
answer.code:21:41: error: invalid conversion from ‘int (*)(const char*, const char*) noexcept’ to ‘int’ [-fpermissive]
   21 |   for(int now=head[x]; now; now=link[now]) {
      |                                 ~~~~~~~~^
      |                                         |
      |                                         int (*)(const char*, const char*) noexcept