Language: C++

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define rep(i, n) for (ll i = 0; i < n; i++)
#define FOR(i, a, b) for (ll i = a; i < b; i++)
#define is(a, b) a == b
#define len(v) ll(v.size())

class UnionFind {
public:
	vector<int> par;//親の番号
    vector<int> rank;//木の深さ
 
	UnionFind(int n){//全ての要素に対して自身が根となるように初期化, 木の深さは0になる
		rep(i,n){
            par.push_back(i);
            rank.push_back(0);
        }
	}
 
	int find(int x) {//木の根を求める
		if(par[x]==x){
            return x;
        }else{
            return par[x]=find(par[x]);
        }
	}
 
	void unite(int x,int y){//xとyの属する集合を併合
        x=find(x);
        y=find(y);
        if(x==y) return;
        if(rank[x]<rank[y]){//木の深さが小さい方を大きい方へ繋げる
            par[x]=y;
        }else{
            par[y]=x;
            if(rank[x]==rank[y]) rank[x]++;
        }
    }

    bool same(int x,int y){//xとyが同じ集合に属するか否か
        return find(x)==find(y);
    }
};
//x以下の要素への最小index, ソートしてから使ってね
template <class T> 
int former(const vector<T> &v, T x){
  return upper_bound(v.begin(), v.end(), x) - v.begin() - 1;
}
//x以上の要素への最小index
template <class T> 
int latter(const vector<T> &v, T x){
  return lower_bound(v.begin(), v.end(), x) - v.begin();
}
//vector書き出し
template <class T>
void cout_vec(const vector<T> &vec1){
  rep(i,len(vec1)){
    cout<<vec1[i]<<' ';
  }
  cout<<'\n';
}
//nCk
template <class T>
T comb(T n,T k){
    T ans=1;
    FOR(i,n-k+1,n+1){
        ans*=i;
    }
    FOR(i,1,k+1){
        ans/=i;
    }
    return ans;
}
//a,bの最大公約数
template <class T>
T gcd(T a,T b) {
	if (b == 0) return a;
	else return gcd(b, a % b);
}
//素因数分解
template <class T>
map<T,T> prime_factor(T x){
    map<T,T> ans;
    for(T i=2;i*i<=x;i++){
        while(x%i==0){
            x/=i;
            ans[i]++;
        }
    }
    if (x!=1){
        ans[x]=1;
    }
    return ans;
}
//約数列挙
template <class T>
vector<T> divisor(T x){
    vector<T> res;
    for(T i=1;i*i<=x;i++){
        if(x%i==0){
            res.push_back(i);
            if(i!=x/i){
                res.push_back(x/i);
            }
        }
    }
    return res;
}
//素数判定
template <class T>
bool is_prime(T x){
    for(T i=2;i*i<=x;i++){
        if(x%i==0){
            return false;
        }
    }
    return x!=1;
}

const ll inf=1e9+7;

ll mult(ll n,ll m){//n^m%infを求める
    if(m==1){
        return n%inf;
    }else if(m%2==0){//オーバーフロー防止のためにn^(m/2)*n^(m/2)を考える
        ll t=mult(n,m/2);
        return (t*t)%inf;
    }else{//奇数の時はn^(m-1)*nを考える
        ll t=mult(n,m-1);
        return (t*n)%inf;
    }
}

typedef pair<int,int> P;
int h,w;
int cnt=0;//初めの状態の白の個数
int in=pow(10,6);
int ans=0;
vector<vector<char>> ma(1010,vector<char>(1010));
vector<vector<int>> d(1010,vector<int>(1010,in));
deque<P> que;
vector<int> dx={1,0,-1,0};
vector<int> dy={0,1,0,-1};

void bfs(){
    d[1][1]=0;
    que.push_back(P(1,1));
    while(!que.empty()){
        P p=que.front();
        que.pop_front();
        if(p.first==h && p.second==w){
            break;
        }
        rep(i,4){
            int nx=p.first+dx[i];
            int ny=p.second+dy[i];
            if(1<=nx && nx<=h && 1<=ny && ny<=w && ma[nx][ny]!='#' && d[nx][ny]==in){
                que.push_back(P(nx,ny));
                d[nx][ny]=d[p.first][p.second]+1;
            }
        }
    }
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin>>h>>w;
    FOR(i,1,h+1){
        FOR(j,1,w+1){
            cin>>ma[i][j];  
            if(ma[i][j]=='.'){
                cnt++;
            } 
        }
    }
    bfs();
    if(d[h][w]==in){
        cout<<-1<<end;
    }else{
        cout<<cnt-(d[h][w]+1)<<endl;
    }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:181:17: error: no match for 'operator<<' (operand types are 'std::basic_ostream<char>' and '<unresolved overloaded function type>')
  181 |         cout<<-1<<end;
      |         ~~~~~~~~^~~~~
In file included from /usr/include/c++/14/istream:41,
                 from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127,
                 from a.cc:1:
/usr/include/c++/14/ostream:116:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(__ostream_type& (*)(__ostream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  116 |       operator<<(__ostream_type& (*__pf)(__ostream_type&))
      |       ^~~~~~~~
/usr/include/c++/14/ostream:116:36: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'std::basic_ostream<char>::__ostream_type& (*)(std::basic_ostream<char>::__ostream_type&)' {aka 'std::basic_ostream<char>& (*)(std::basic_ostream<char>&)'}
  116 |       operator<<(__ostream_type& (*__pf)(__ostream_type&))
      |                  ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/ostream:125:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(__ios_type& (*)(__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>; __ios_type = std::basic_ios<char>]'
  125 |       operator<<(__ios_type& (*__pf)(__ios_type&))
      |       ^~~~~~~~
/usr/include/c++/14/ostream:125:32: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'std::basic_ostream<char>::__ios_type& (*)(std::basic_ostream<char>::__ios_type&)' {aka 'std::basic_ios<char>& (*)(std::basic_ios<char>&)'}
  125 |       operator<<(__ios_type& (*__pf)(__ios_type&))
      |                  ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
/usr/include/c++/14/ostream:135:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  135 |       operator<<(ios_base& (*__pf) (ios_base&))
      |       ^~~~~~~~
/usr/include/c++/14/ostream:135:30: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'std::ios_base& (*)(std::ios_base&)'
  135 |       operator<<(ios_base& (*__pf) (ios_base&))
      |                  ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
/usr/include/c++/14/ostream:174:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  174 |       operator<<(long __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:174:23: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'long int'
  174 |       operator<<(long __n)
      |                  ~~~~~^~~
/usr/include/c++/14/ostream:178:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  178 |       operator<<(unsigned long __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:178:32: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'long unsigned int'
  178 |       operator<<(unsigned long __n)
      |                  ~~~~~~~~~~~~~~^~~
/usr/include/c++/14/ostream:182:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  182 |       operator<<(bool __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:182:23: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'bool'
  182 |       operator<<(bool __n)
      |                  ~~~~~^~~
In file included from /usr/include/c++/14/ostream:1022:
/usr/include/c++/14/bits/ostream.tcc:96:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char; _Traits = std::char_traits<char>]'
   96 |     basic_ostream<_CharT, _Traits>::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/ostream.tcc:97:22: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'short int'
   97 |     operator<<(short __n)
      |                ~~~~~~^~~
/usr/include/c++/14/ostream:189:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  189 |       operator<<(unsigned short __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:189:33: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'short unsigned int'
  189 |       operator<<(unsigned short __n)
      |                  ~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/ostream.tcc:110:5: note: candidate: 'std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char; _Traits = std::char_traits<char>]'
  110 |     basic_ostream<_CharT, _Traits>::
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/ostream.tcc:111:20: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'int'
  111 |     operator<<(int __n)
      |                ~~~~^~~
/usr/include/c++/14/ostream:200:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  200 |       operator<<(unsigned int __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:200:31: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'unsigned int'
  200 |       operator<<(unsigned int __n)
      |                  ~~~~~~~~~~~~~^~~
/usr/include/c++/14/ostream:211:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  211 |       operator<<(long long __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:211:28: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'long long int'
  211 |       operator<<(long long __n)
      |                  ~~~~~~~~~~^~~
/usr/include/c++/14/ostream:215:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  215 |       operator<<(unsigned long long __n)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:215:37: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'long long unsigned int'
  215 |       operator<<(unsigned long long __n)
      |                  ~~~~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/ostream:231:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  231 |       operator<<(double __f)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:231:25: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'double'
  231 |       operator<<(double __f)
      |                  ~~~~~~~^~~
/usr/include/c++/14/ostream:235:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  235 |       operator<<(float __f)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:235:24: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'float'
  235 |       operator<<(float __f)
      |                  ~~~~~~^~~
/usr/include/c++/14/ostream:243:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  243 |       operator<<(long double __f)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:243:30: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'long double'
  243 |       operator<<(long double __f)
      |                  ~~~~~~~~~~~~^~~
/usr/include/c++/14/ostream:301:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>]'
  301 |       operator<<(const void* __p)
      |       ^~~~~~~~
/usr/include/c++/14/ostream:301:30: note:   no known conversion for argument 1 from '<unresolved overloaded function type>' to 'const void*'
  301 |       operator<<(const void* __p)
      |                  ~~~~~~~~~~~~^~~
/usr/include/c++/14/ostream:306:7: note: candidate: 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::nullptr_t) [with _CharT = char; _Traits = std::char_traits<char>; __ostream_type = std::basic_ostream<char>; std::nullptr_t = std::nullptr_t]'
  306 |