Language: C++

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define dd double
#define endl "\n"
#define pb push_back
#define all(v) v.begin(),v.end()
#define mp make_pair
#define fi first
#define se second
#define fo(i,n) for(int i=0;i<n;i++)
#define fo1(i,n) for(int i=1;i<=n;i++)
ll mod=1000000007;
ll n,k,t,m,q,flag=0;
ll po(ll k ,ll n,ll ans,ll temp,ll ans1){
    if(n==0)return ans;
    while(temp<=n){
        ans*=ans1;ans%=mod;ans1=ans1*ans1;ans1%=mod;n=n-temp;temp*=2;
    }
    return po(k,n,ans,1,k)%mod;
    //eg. po(2,78,1,1,2);
}
string s1,s2;
vector<string>dp[30001][30001] ;
string ans(ll a,ll b){
    if(a==0||b==0){string s; return s;}
    if(dp[a][b]!="*")return dp[a][b] ;
  if(s1[a-1]==s2[b-1]){
    string s=ans(a-1,b-1);
    s.pb(s1[a-1]);
    return dp[a][b] = s;
  }
  else {
    string sa=ans(a,b-1);
    string sb=ans(a-1,b);
    if(sa.size()>sb.size()){
        return dp[a][b] = sa;
    }
    else return dp[a][b] = sb;
  }
}

ll min(ll a,ll b){if(a>b)return b;else return a;}
ll max(ll a,ll b){if(a>b)return a;else return b;}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    
    t=1;
    for(int i=0 ; i<=3000 ; i++){
        for(int j=0 ; j<=3000 ; j++){
            dp[i][j] = '*' ;
        }
    }
    while(t--){
        cin>>s1>>s2;
        cout<<ans(s1.size(),s2.size());
        
    }

    return 0;
}


Compiler output:
a.cc: In function 'std::string ans(long long int, long long int)':
a.cc:27:16: error: no match for 'operator!=' (operand types are 'std::vector<std::__cxx11::basic_string<char> >' and 'const char [2]')
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |        ~~~~~~~~^~~~~
      |               |  |
      |               |  const char [2]
      |               std::vector<std::__cxx11::basic_string<char> >
In file included from /usr/include/c++/14/regex:68,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:181,
                 from a.cc:1:
/usr/include/c++/14/bits/regex.h:1132:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1132 |     operator!=(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1132:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
/usr/include/c++/14/bits/regex.h:1212:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator!=(__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const sub_match<_BiIter>&)'
 1212 |     operator!=(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1212:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
/usr/include/c++/14/bits/regex.h:1305:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)'
 1305 |     operator!=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1305:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
/usr/include/c++/14/bits/regex.h:1379:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1379 |     operator!=(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1379:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'const char [2]'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
/usr/include/c++/14/bits/regex.h:1473:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1473 |     operator!=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1473:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
/usr/include/c++/14/bits/regex.h:1547:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1547 |     operator!=(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1547:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'const char [2]'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
/usr/include/c++/14/bits/regex.h:1647:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1647 |     operator!=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1647:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
/usr/include/c++/14/bits/regex.h:2213:5: note: candidate: 'template<class _Bi_iter, class _Alloc> bool std::__cxx11::operator!=(const match_results<_BiIter, _Alloc>&, const match_results<_BiIter, _Alloc>&)'
 2213 |     operator!=(const match_results<_Bi_iter, _Alloc>& __m1,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:2213:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::__cxx11::match_results<_BiIter, _Alloc>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
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:
/usr/include/c++/14/bits/stl_pair.h:1052:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator!=(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1052 |     operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1052:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::pair<_T1, _T2>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:455:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  455 |     operator!=(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:455:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::reverse_iterator<_Iterator>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
/usr/include/c++/14/bits/stl_iterator.h:500:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  500 |     operator!=(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:500:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::reverse_iterator<_Iterator>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1686 |     operator!=(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::move_iterator<_IteratorL>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1753 |     operator!=(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::move_iterator<_IteratorL>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
In file included from /usr/include/c++/14/bits/char_traits.h:42,
                 from /usr/include/c++/14/string:42,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/bits/postypes.h:197:5: note: candidate: 'template<class _StateT> bool std::operator!=(const fpos<_StateT>&, const fpos<_StateT>&)'
  197 |     operator!=(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:197:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::fpos<_StateT>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
In file included from /usr/include/c++/14/string:43:
/usr/include/c++/14/bits/allocator.h:243:5: note: candidate: 'template<class _T1, class _T2> bool std::operator!=(const allocator<_CharT>&, const allocator<_T2>&)'
  243 |     operator!=(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:243:5: note:   template argument deduction/substitution failed:
a.cc:27:18: note:   'std::vector<std::__cxx11::basic_string<char> >' is not derived from 'const std::allocator<_CharT>'
   27 |     if(dp[a][b]!="*")return dp[a][b] ;
      |                  ^~~
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:651:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(basic_string_view<_Ch