Language: C++

 #include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cctype>
#include <cassert>
#include <climits>
#include <string>
#include <bitset>
#include <cfloat>
#include <unordered_set>
#include <iomanip>
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int,int> > vpii;
typedef vector<vector<int> > vvi;
typedef vector<vector<char> > vvc;
typedef vector<vector<string> > vvs;
typedef vector<vector<ll> > vvll;
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define irep(it, stl) for(auto it = stl.begin(); it != stl.end(); it++)
#define drep(i,n) for(int i = (n) - 1; i >= 0; --i)
#define fin(ans) cout << (ans) << endl
#define mp(p,q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
int dx8[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int dy8[8] = {0, 1, 0, -1, 1, 1, -1, -1};
int dx4[4] = {1, 0, -1, 0};
int dy4[4] = {0, 1, 0, -1};
template <class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;} return 0;}
template <class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;} return 0;}
template<typename A, size_t N, typename T> void Fill(A (&array)[N], const T &val){ fill((T*)array, (T*)(array+N), val); }
struct io{io(){ios::sync_with_stdio(false);cin.tie(0);}};
const int INF = INT_MAX;
const ll LLINF = 1LL<<60;
const ll MOD = 1000000007;
const double EPS = 1e-9;
template < typename T > inline string toString( const T &a ) { ostringstream oss; oss << a; return oss.str(); };



int H,W;
vs S;
int left[2010][2010],right[2010][2010],up[2010][2010],down[2010][2010];

int main()
{
  cin >> H >> W;
  S.resize(H);
  rep(i,H) cin >> S[i];
  

  //left
  rep(i,H){
      int cur = 0;
      rep(j,W){
          //...#..#..みたいな感じだと例えばi=0なら自分含めて3マス進んで壁に当たるからS[0]=3が入る,壁は0が入る
          if(S[i][j] == '#') cur=0;
          else cur++;
          left[i][j] = cur;
      }
  }

  //right
  rep(i,H){
      int cur=0;
      for (int j = W-1; j <=0; j--)
      {
          if(S[i][j] == '#') cur=0;
          else cur++;
          right[i][j] = cur;
      }
  }

  //down
  rep(j,W){
      int cur=0;
      rep(i,H){
          if(S[i][j] == '#') cur=0;
          else cur++;
          down[i][j] = cur;
      } 
  }
   //up
   rep(j,W){
      int cur=0;
     for(int i=H-1;i<=0;i--){
          if(S[i][j] == '#') cur=0;
          else cur++;
          up[i][j] = cur;
      } 
  }
  
  int ans=0;
  
  rep(i,H){
      rep(j,W){
          ans = max(ans,left[i][j]+right[i][j]+up[i][j]+down[i][j]-3);//-3は注目しているマスが4個重複するので-3
      }
  }

  fin(ans);
  
}



Compiler output:
a.cc: In function 'int main()':
a.cc:82:11: error: reference to 'left' is ambiguous
   82 |           left[i][j] = cur;
      |           ^~~~
In file included from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/ios_base.h:1062:3: note: candidates are: 'std::ios_base& std::left(ios_base&)'
 1062 |   left(ios_base& __base)
      |   ^~~~
a.cc:66:5: note:                 'int left [2010][2010]'
   66 | int left[2010][2010],right[2010][2010],up[2010][2010],down[2010][2010];
      |     ^~~~
a.cc:93:11: error: reference to 'right' is ambiguous
   93 |           right[i][j] = cur;
      |           ^~~~~
/usr/include/c++/14/bits/ios_base.h:1070:3: note: candidates are: 'std::ios_base& std::right(ios_base&)'
 1070 |   right(ios_base& __base)
      |   ^~~~~
a.cc:66:22: note:                 'int right [2010][2010]'
   66 | int left[2010][2010],right[2010][2010],up[2010][2010],down[2010][2010];
      |                      ^~~~~
a.cc:120:25: error: reference to 'left' is ambiguous
  120 |           ans = max(ans,left[i][j]+right[i][j]+up[i][j]+down[i][j]-3);//-3は注目しているマスが4個重複するので-3
      |                         ^~~~
/usr/include/c++/14/bits/ios_base.h:1062:3: note: candidates are: 'std::ios_base& std::left(ios_base&)'
 1062 |   left(ios_base& __base)
      |   ^~~~
a.cc:66:5: note:                 'int left [2010][2010]'
   66 | int left[2010][2010],right[2010][2010],up[2010][2010],down[2010][2010];
      |     ^~~~
a.cc:120:36: error: reference to 'right' is ambiguous
  120 |           ans = max(ans,left[i][j]+right[i][j]+up[i][j]+down[i][j]-3);//-3は注目しているマスが4個重複するので-3
      |                                    ^~~~~
/usr/include/c++/14/bits/ios_base.h:1070:3: note: candidates are: 'std::ios_base& std::right(ios_base&)'
 1070 |   right(ios_base& __base)
      |   ^~~~~
a.cc:66:22: note:                 'int right [2010][2010]'
   66 | int left[2010][2010],right[2010][2010],up[2010][2010],down[2010][2010];
      |                      ^~~~~