Language: C++

#include<bits/stdc++.h>
using namespace std;
int main(){
  int h,w,n=0;cin>>h>>w;
  vector<vector<char>>a(h,vector<char>(w));
  for(int i=0;i<h;i++){
    for(int j=0;j<w;j++){
      cin>>a.at(i).at(j);
      if(a.at(i).at(j)=='#')n++;
    }
  }
  if(n!=h+w-1)cout<<"Impossible"<<endl;
  else{
    vector<pair<int,int>>p(n);
    int s=0;
    for(int i=0;i<h;i++){
      for(int j=0;j<w;j++){
        if(a.at(i).at(j)=='#'){
          p.at(s)=(j,i);
          s++;
        }
        if(s==n-1)break;
      }
    }
    int t=0;
    for(int i=0;i<n-1;i++){
      if(p.at(i)>p.at(i+1)){
        t++;
        break;
      }
    }
    if(t>0)coutt<<"Impossible"<<endl;
    else cout<<"Possible"<<endl;
  }
}
      
         
           


Compiler output:
a.cc: In function 'int main()':
a.cc:19:23: error: no match for 'operator=' (operand types are '__gnu_cxx::__alloc_traits<std::allocator<std::pair<int, int> >, std::pair<int, int> >::value_type' {aka 'std::pair<int, int>'} and 'int')
   19 |           p.at(s)=(j,i);
      |                       ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_pair.h:946:9: note: candidate: 'template<class _U1, class _U2> typename std::enable_if<std::__and_<std::is_assignable<_T1&, const _U1&>, std::is_assignable<_T2&, const _U2&> >::value, std::pair<_T1, _T2>&>::type std::pair<_T1, _T2>::operator=(const std::pair<_U1, _U2>&) [with _U2 = _U1; _T1 = int; _T2 = int]'
  946 |         operator=(const pair<_U1, _U2>& __p)
      |         ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:946:9: note:   template argument deduction/substitution failed:
a.cc:19:23: note:   mismatched types 'const std::pair<_T1, _T2>' and 'int'
   19 |           p.at(s)=(j,i);
      |                       ^
/usr/include/c++/14/bits/stl_pair.h:957:9: note: candidate: 'template<class _U1, class _U2> typename std::enable_if<std::__and_<std::is_assignable<_T1&, _U1&&>, std::is_assignable<_T2&, _U2&&> >::value, std::pair<_T1, _T2>&>::type std::pair<_T1, _T2>::operator=(std::pair<_U1, _U2>&&) [with _U2 = _U1; _T1 = int; _T2 = int]'
  957 |         operator=(pair<_U1, _U2>&& __p)
      |         ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:957:9: note:   template argument deduction/substitution failed:
a.cc:19:23: note:   mismatched types 'std::pair<_T1, _T2>' and 'int'
   19 |           p.at(s)=(j,i);
      |                       ^
/usr/include/c++/14/bits/stl_pair.h:921:7: note: candidate: 'std::pair<_T1, _T2>& std::pair<_T1, _T2>::operator=(std::__conditional_t<((bool)std::__and_<std::is_copy_assignable<_T1>, std::is_copy_assignable<_T2> >::value), const std::pair<_T1, _T2>&, const std::__nonesuch&>) [with _T1 = int; _T2 = int; std::__conditional_t<((bool)std::__and_<std::is_copy_assignable<_T1>, std::is_copy_assignable<_T2> >::value), const std::pair<_T1, _T2>&, const std::__nonesuch&> = const std::pair<int, int>&]'
  921 |       operator=(__conditional_t<__and_<is_copy_assignable<_T1>,
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:923:65: note:   no known conversion for argument 1 from 'int' to 'std::__conditional_t<true, const std::pair<int, int>&, const std::__nonesuch&>' {aka 'const std::pair<int, int>&'}
  921 |       operator=(__conditional_t<__and_<is_copy_assignable<_T1>,
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
  922 |                                        is_copy_assignable<_T2>>::value,
      |                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  923 |                                 const pair&, const __nonesuch&> __p)
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_pair.h:931:7: note: candidate: 'std::pair<_T1, _T2>& std::pair<_T1, _T2>::operator=(std::__conditional_t<((bool)std::__and_<std::is_move_assignable<_Tp>, std::is_move_assignable<_T2> >::value), std::pair<_T1, _T2>&&, std::__nonesuch&&>) [with _T1 = int; _T2 = int; std::__conditional_t<((bool)std::__and_<std::is_move_assignable<_Tp>, std::is_move_assignable<_T2> >::value), std::pair<_T1, _T2>&&, std::__nonesuch&&> = std::pair<int, int>&&]'
  931 |       operator=(__conditional_t<__and_<is_move_assignable<_T1>,
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:933:55: note:   no known conversion for argument 1 from 'int' to 'std::__conditional_t<true, std::pair<int, int>&&, std::__nonesuch&&>' {aka 'std::pair<int, int>&&'}
  931 |       operator=(__conditional_t<__and_<is_move_assignable<_T1>,
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  932 |                                        is_move_assignable<_T2>>::value,
      |                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  933 |                                 pair&&, __nonesuch&&> __p)
      |                                 ~~~~~~~~~~~~~~~~~~~~~~^~~
a.cc:32:12: error: 'coutt' was not declared in this scope
   32 |     if(t>0)coutt<<"Impossible"<<endl;
      |            ^~~~~