Language: C++

#include <bits/stdc++.h>
#define ll long long int
#define pb push_back
#define st first
#define nd second
#define pii pair<int,int>

using namespace std;

const int nax = 1005;
char a[nax][nax];
int n,m;

int x1,y1;
int x2,y2;

int par[nax * nax];

int f(int v)
{
    if(par[v] == v) return v;
    return par[v] = f(par[v]);
}

void u(int x,int y)
{
    x = f(x);
    y = f(y);
    if(x == y) return;
    if(rand()%2) swap(x,y);
    par[x] = y;
}

vector<int> adj[nax * nax];

int d[nax * nax];
bool vis[nax * nax];

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0);
    cin>>n>>m;
    cin>>x1>>y1;
    cin>>x2>>y2;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            cin>>a[i][j];
            par[i*m+j] = i * m + j;
        }
    }
    vector<int> dx = {-1,1,0,0};
    vector<int> dy = {0,0,-1,1};
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            for(int k=0;k<4;k++)
            {
                int x = dx[k];
                int y = dy[k];
                x += i;
                y += j;
                if(x >= 1 && x <= n && y >= 1 && y <= m)
                {
                    if(a[x][y] == '.' && a[i][j] == '.')
                    {
                        u(x * m + y,i * m + j);
                    }
                }
            }
        }
    }

    vector<int> go1 = {-2,-1,0,1,2};

    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            for(int x=-2;x<=2;x++)
            {
                for(int y=-2;y<=2;y++)
                {
                    if(x == 0 && y == 0) continue;
                    int xd = x + i;
                    int yd = y + j;
                    if(xd < 1 || xd > n || yd < 1 || yd > m) continue;
                    if(a[i][j] != '.' || a[xd][yd] != '.') continue;
                    if(f(i * m + j) != f(xd * m + yd))
                    {
                        int s1 = f(i*m+j);
                        int s2 = f(xd*m+yd);
                        adj[s1].pb(s2);
                        adj[s2].pb(s1);
                    }
                }
            }
        }
    }

    int s1 = f(x1 * m + y1);
    int s2 = f(x2 * m + y2);
    vector<int> bfs;
    int wsk = 0;
    bfs.pb(s1);
    vis[s1] = true;
    while(wsk < bfs.size())
    {
        int akt = bfs[wsk++];
        for(auto x : adj[akt])
        {
            if(vis[x] == false)
            {
                d[x] = d[akt] + 1;
                vis[x] = true;
                bfs.pb(x);
            }
        }
    }

    if(vis[s2] == false) cout<<-1;
    else cout<<d[s2]<<endl;

    return 0;
}


Compiler output:
a.cc:14:8: error: 'int y1' redeclared as different kind of entity
   14 | int x1,y1;
      |        ^~
In file included from /usr/include/features.h:523,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/os_defines.h:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/c++config.h:683,
                 from /usr/include/c++/14/cassert:43,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:33,
                 from a.cc:1:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:257:1: note: previous declaration 'double y1(double)'
  257 | __MATHCALL (y1,, (_Mdouble_));
      | ^~~~~~~~~~
a.cc: In function 'int main()':
a.cc:43:12: error: no match for 'operator>>' (operand types are 'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} and 'double(double) noexcept')
   43 |     cin>>x1>>y1;
      |     ~~~~~~~^~~~
      |        |     |
      |        |     double(double) noexcept
      |        std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}
In file included 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:
/usr/include/c++/14/istream:170:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  170 |       operator>>(bool& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:170:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: cannot bind non-const lvalue reference of type 'bool&' to a value of type 'double (*)(double) noexcept'
   43 |     cin>>x1>>y1;
      |              ^~
/usr/include/c++/14/istream:174:7: note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char; _Traits = std::char_traits<char>]' (near match)
  174 |       operator>>(short& __n);
      |       ^~~~~~~~
/usr/include/c++/14/istream:174:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'short int' [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
a.cc:43:14: error: cannot bind rvalue '(short int)y1' to 'short int&'
/usr/include/c++/14/istream:177:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  177 |       operator>>(unsigned short& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:177:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'short unsigned int' [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
a.cc:43:14: error: cannot bind rvalue '(short unsigned int)y1' to 'short unsigned int&'
/usr/include/c++/14/istream:181:7: note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char; _Traits = std::char_traits<char>]' (near match)
  181 |       operator>>(int& __n);
      |       ^~~~~~~~
/usr/include/c++/14/istream:181:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'int' [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
a.cc:43:14: error: cannot bind rvalue '(int)y1' to 'int&'
/usr/include/c++/14/istream:184:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  184 |       operator>>(unsigned int& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:184:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'unsigned int' [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
a.cc:43:14: error: cannot bind rvalue '(unsigned int)y1' to 'unsigned int&'
/usr/include/c++/14/istream:188:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  188 |       operator>>(long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:188:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'long int' [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
a.cc:43:14: error: cannot bind rvalue '(long int)y1' to 'long int&'
/usr/include/c++/14/istream:192:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  192 |       operator>>(unsigned long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:192:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'long unsigned int' [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
a.cc:43:14: error: cannot bind rvalue '(long unsigned int)y1' to 'long unsigned int&'
/usr/include/c++/14/istream:199:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  199 |       operator>>(long long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:199:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'long long int' [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
a.cc:43:14: error: cannot bind rvalue '(long long int)y1' to 'long long int&'
/usr/include/c++/14/istream:203:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  203 |       operator>>(unsigned long long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:203:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'long long unsigned int' [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
a.cc:43:14: error: cannot bind rvalue '(long long unsigned int)y1' to 'long long unsigned int&'
/usr/include/c++/14/istream:328:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  328 |       operator>>(void*& __p)
      |       ^~~~~~~~
/usr/include/c++/14/istream:328:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'void*' [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
a.cc:43:14: error: cannot bind rvalue '(void*)y1' to 'void*&'
/usr/include/c++/14/istream:122:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(__istream_type& (*)(__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  122 |       operator>>(__istream_type& (*__pf)(__istream_type&))
      |       ^~~~~~~~
/usr/include/c++/14/istream:122:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&)' {aka 'std::basic_istream<char>& (*)(std::basic_istream<char>&)'} [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
/usr/include/c++/14/istream:126:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(__ios_type& (*)(__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>; __ios_type = std::basic_ios<char>]' (near match)
  126 |       operator>>(__ios_type& (*__pf)(__ios_type&))
      |       ^~~~~~~~
/usr/include/c++/14/istream:126:7: note:   conversion of argument 1 would be ill-formed:
a.cc:43:14: error: invalid conversion from 'double (*)(double) noexcept' to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&)' {aka 'std::basic_ios<char>& (*)(std::basic_ios<char>&)'} [-fpermissive]
   43 |     cin>>x1>>y1;
      |              ^~
      |              |
      |              double (*)(double) noexcept
/usr/include/c++/14/istream:133:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::o