Language: C++

#include <iostream>
#include <iomanip>
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <utility>
#include <cmath>
#include <tuple>
#include <queue>
#include <bitset>
#include <set>
#include <map>
#include <list>

using ll = long long;
using ld = long double;
using namespace std;
const int INF = 1e9+100;
const ll INF64 = 7e18l;
const int mod = 1000000007;
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define ALL(a) (a).begin(), (a).end()
#define FIN ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);


int dx[4] = {1,0,-1,0};
int dy[4] = {0,1,0,-1};

int bfs(const vector<string> *v,int x,int y){
    int H = v.size();
    int W = v[0].size();
    vector<vector<int>> dist(H,vector<int>(W,-1));
    queue<pair<int,int>> que;

    int res = 0;
    que.push({x,y});
    dist[x][y] = 0;
    while(!que.empty()){
        int x = que.front().first, y = que.front().second;
        res = max(res,dist[x][y]);
        que.pop();
        for(int dir=0; dir<4;dir++){
            int nx = x + dx[dir], ny = y + dy[dir];
            if(nx<0 || nx >= H || ny < 0 || ny >= W) continue;
            if(v[nx][ny] == '#') continue;
            if(dist[nx][ny] == -1){
                dist[nx][ny] = dist[x][y] + 1;
                que.push({nx,ny});
            }
        }
    }
    return res;
}


int main(){
    FIN;
    int H,W;
    cin >> H >> W;
    vector<string> v(H);
    for(int i=0;i<H;i++) cin >> v[i];

    int ans = 0;
    for(int x=0;x<H;x++){
        for(int y=0;y<W;y++){
            if(v[x][y] == '#') continue;
            ans = max(ans,bfs(v,x,y));
        }
    }

    cout << ans << endl;
    return 0;
}

Compiler output:
a.cc: In function 'int bfs(const std::vector<std::__cxx11::basic_string<char> >*, int, int)':
a.cc:31:15: error: request for member 'size' in 'v', which is of pointer type 'const std::vector<std::__cxx11::basic_string<char> >*' (maybe you meant to use '->' ?)
   31 |     int H = v.size();
      |               ^~~~
a.cc:46:26: error: no match for 'operator==' (operand types are 'const __gnu_cxx::__alloc_traits<std::allocator<std::__cxx11::basic_string<char> >, std::__cxx11::basic_string<char> >::value_type' {aka 'const std::__cxx11::basic_string<char>'} and 'char')
   46 |             if(v[nx][ny] == '#') continue;
In file included from /usr/include/c++/14/iosfwd:42,
                 from /usr/include/c++/14/ios:40,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/postypes.h:192:5: note: candidate: 'template<class _StateT> bool std::operator==(const fpos<_StateT>&, const fpos<_StateT>&)'
  192 |     operator==(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:192:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   'const __gnu_cxx::__alloc_traits<std::allocator<std::__cxx11::basic_string<char> >, std::__cxx11::basic_string<char> >::value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const std::fpos<_StateT>'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
In file included from /usr/include/c++/14/string:43,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44:
/usr/include/c++/14/bits/allocator.h:235:5: note: candidate: 'template<class _T1, class _T2> bool std::operator==(const allocator<_CharT>&, const allocator<_T2>&)'
  235 |     operator==(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:235:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   'const __gnu_cxx::__alloc_traits<std::allocator<std::__cxx11::basic_string<char> >, std::__cxx11::basic_string<char> >::value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const std::allocator<_CharT>'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
In file included from /usr/include/c++/14/string:48:
/usr/include/c++/14/bits/stl_iterator.h:441:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  441 |     operator==(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:441:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   'const __gnu_cxx::__alloc_traits<std::allocator<std::__cxx11::basic_string<char> >, std::__cxx11::basic_string<char> >::value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  486 |     operator==(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   'const __gnu_cxx::__alloc_traits<std::allocator<std::__cxx11::basic_string<char> >, std::__cxx11::basic_string<char> >::value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1667 |     operator==(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   'const __gnu_cxx::__alloc_traits<std::allocator<std::__cxx11::basic_string<char> >, std::__cxx11::basic_string<char> >::value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1737 |     operator==(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   'const __gnu_cxx::__alloc_traits<std::allocator<std::__cxx11::basic_string<char> >, std::__cxx11::basic_string<char> >::value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/string:51:
/usr/include/c++/14/bits/stl_pair.h:1033:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator==(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1033 |     operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1033:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   'const __gnu_cxx::__alloc_traits<std::allocator<std::__cxx11::basic_string<char> >, std::__cxx11::basic_string<char> >::value_type' {aka 'const std::__cxx11::basic_string<char>'} is not derived from 'const std::pair<_T1, _T2>'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:629:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator==(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  629 |     operator==(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:629:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   'std::__cxx11::basic_string<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
/usr/include/c++/14/string_view:637:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator==(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  637 |     operator==(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:637:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   'std::__cxx11::basic_string<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
/usr/include/c++/14/string_view:644:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator==(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  644 |     operator==(__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:644:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'char'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
/usr/include/c++/14/bits/basic_string.h:3755:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3755 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3755:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'char'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
/usr/include/c++/14/bits/basic_string.h:3772:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3772 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3772:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   mismatched types 'const _CharT*' and 'char'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
/usr/include/c++/14/bits/basic_string.h:3819:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3819 |     operator==(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3819:5: note:   template argument deduction/substitution failed:
a.cc:46:29: note:   mismatched types 'const _CharT*' and 'std::__cxx11::basic_string<char>'
   46 |             if(v[nx][ny] == '#') continue;
      |                             ^~~
In file included from /usr/include/c++/14/bits/memory_resource.h:47,
                 from /usr/include/c++/14/string:68:
/usr/include/c++/14/tuple:2558:5: note: candidate: 'template<class ... _TElements,