Language: C++

#include<bits/stdc++.h>
using namespace std;
using ll=long long int;
#define rep(i,n) for(int i=0;i<(n);i++)

int main(){
    long long int s;
    cin>>s;
    vector<map<long long int,long long int>>a[1000000];
    a.at(0)[0]=s; 
    a[0][1]=1;
    for(long long int i=1;i<1000000;i++){
        if(a[i-1][0]%2==0){
            a[i][0]=a[i-1][1]/2;
            a[i][1]=i+1;
        }
        else {
            a[i][0]=3*a[i-1][0]+1;
            a[i][1]=i+1;
        }

    }
    sort(a.begin(),a.end());
    for(long long int i=1;i<1000000;i++){
        if(a[i][0]==a[i-1][0] && a[i][1]>a[i-1][1] ){
            cout<<a[i][1]<<endl;
            return 0;
        }
    }
}


Compiler output:
a.cc: In function 'int main()':
a.cc:10:7: error: request for member 'at' in 'a', which is of non-class type 'std::vector<std::map<long long int, long long int> > [1000000]'
   10 |     a.at(0)[0]=s;
      |       ^~
a.cc:11:13: error: no match for 'operator=' (operand types are '__gnu_cxx::__alloc_traits<std::allocator<std::map<long long int, long long int> >, std::map<long long int, long long int> >::value_type' {aka 'std::map<long long int, long long int>'} and 'int')
   11 |     a[0][1]=1;
      |             ^
In file included from /usr/include/c++/14/map:63,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:152,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_map.h:331:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>& std::map<_Key, _Tp, _Compare, _Alloc>::operator=(const std::map<_Key, _Tp, _Compare, _Alloc>&) [with _Key = long long int; _Tp = long long int; _Compare = std::less<long long int>; _Alloc = std::allocator<std::pair<const long long int, long long int> >]'
  331 |       operator=(const map&) = default;
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:331:17: note:   no known conversion for argument 1 from 'int' to 'const std::map<long long int, long long int>&'
  331 |       operator=(const map&) = default;
      |                 ^~~~~~~~~~
/usr/include/c++/14/bits/stl_map.h:335:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>& std::map<_Key, _Tp, _Compare, _Alloc>::operator=(std::map<_Key, _Tp, _Compare, _Alloc>&&) [with _Key = long long int; _Tp = long long int; _Compare = std::less<long long int>; _Alloc = std::allocator<std::pair<const long long int, long long int> >]'
  335 |       operator=(map&&) = default;
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:335:17: note:   no known conversion for argument 1 from 'int' to 'std::map<long long int, long long int>&&'
  335 |       operator=(map&&) = default;
      |                 ^~~~~
/usr/include/c++/14/bits/stl_map.h:349:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>& std::map<_Key, _Tp, _Compare, _Alloc>::operator=(std::initializer_list<std::pair<const _Key, _Val> >) [with _Key = long long int; _Tp = long long int; _Compare = std::less<long long int>; _Alloc = std::allocator<std::pair<const long long int, long long int> >]'
  349 |       operator=(initializer_list<value_type> __l)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:349:46: note:   no known conversion for argument 1 from 'int' to 'std::initializer_list<std::pair<const long long int, long long int> >'
  349 |       operator=(initializer_list<value_type> __l)
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
a.cc:13:21: error: no match for 'operator%' (operand types are '__gnu_cxx::__alloc_traits<std::allocator<std::map<long long int, long long int> >, std::map<long long int, long long int> >::value_type' {aka 'std::map<long long int, long long int>'} and 'int')
   13 |         if(a[i-1][0]%2==0){
In file included from /usr/include/c++/14/valarray:605,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166:
/usr/include/c++/14/bits/valarray_after.h:409:5: note: candidate: 'template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__modulus, typename _Dom1::value_type>::result_type> std::operator%(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)'
  409 |     _DEFINE_EXPR_BINARY_OPERATOR(%, struct std::__modulus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note:   template argument deduction/substitution failed:
a.cc:13:22: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::map<long long int, long long int> >, std::map<long long int, long long int> >::value_type' {aka 'std::map<long long int, long long int>'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   13 |         if(a[i-1][0]%2==0){
      |                      ^
/usr/include/c++/14/bits/valarray_after.h:409:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__modulus, typename _Dom1::value_type>::result_type> std::operator%(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)'
  409 |     _DEFINE_EXPR_BINARY_OPERATOR(%, struct std::__modulus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note:   template argument deduction/substitution failed:
a.cc:13:22: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::map<long long int, long long int> >, std::map<long long int, long long int> >::value_type' {aka 'std::map<long long int, long long int>'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   13 |         if(a[i-1][0]%2==0){
      |                      ^
/usr/include/c++/14/bits/valarray_after.h:409:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__modulus, typename _Dom1::value_type>::result_type> std::operator%(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  409 |     _DEFINE_EXPR_BINARY_OPERATOR(%, struct std::__modulus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note:   template argument deduction/substitution failed:
a.cc:13:22: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'int'
   13 |         if(a[i-1][0]%2==0){
      |                      ^
/usr/include/c++/14/bits/valarray_after.h:409:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__modulus, typename _Dom1::value_type>::result_type> std::operator%(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)'
  409 |     _DEFINE_EXPR_BINARY_OPERATOR(%, struct std::__modulus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note:   template argument deduction/substitution failed:
a.cc:13:22: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::map<long long int, long long int> >, std::map<long long int, long long int> >::value_type' {aka 'std::map<long long int, long long int>'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   13 |         if(a[i-1][0]%2==0){
      |                      ^
/usr/include/c++/14/bits/valarray_after.h:409:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__modulus, typename _Dom1::value_type>::result_type> std::operator%(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  409 |     _DEFINE_EXPR_BINARY_OPERATOR(%, struct std::__modulus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:409:5: note:   template argument deduction/substitution failed:
a.cc:13:22: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'int'
   13 |         if(a[i-1][0]%2==0){
      |                      ^
/usr/include/c++/14/valarray:1200:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__modulus, _Tp>::result_type> std::operator%(const valarray<_Tp>&, const valarray<_Tp>&)'
 1200 | _DEFINE_BINARY_OPERATOR(%, __modulus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1200:1: note:   template argument deduction/substitution failed:
a.cc:13:22: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::map<long long int, long long int> >, std::map<long long int, long long int> >::value_type' {aka 'std::map<long long int, long long int>'} is not derived from 'const std::valarray<_Tp>'
   13 |         if(a[i-1][0]%2==0){
      |                      ^
/usr/include/c++/14/valarray:1200:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__modulus, _Tp>::result_type> std::operator%(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)'
 1200 | _DEFINE_BINARY_OPERATOR(%, __modulus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1200:1: note:   template argument deduction/substitution failed:
a.cc:13:22: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::map<long long int, long long int> >, std::map<long long int, long long int> >::value_type' {aka 'std::map<long long int, long long int>'} is not derived from 'const std::valarray<_Tp>'
   13 |         if(a[i-1][0]%2==0){
      |                      ^
/usr/include/c++/14/valarray:1200:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__modulus, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__modulus, _Tp>::result_type> std::operator%(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)'
 1200 | _DEFINE_BINARY_OPERATOR(%, __modulus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1200:1: note:   template argument deduction/substitution failed:
a.cc:13:22: note:   mismatched types 'const std::valarray<_Tp>' and 'int'
   13 |         if(a[i-1][0]%2==0){
      |                      ^
a.cc:14:30: error: no match for 'operator/' (operand types are '__gnu_cxx::__alloc_traits<std::allocator<std::map<long long int, long long int> >, std::map<long long int, long long int> >::value_type' {aka 'std::map<long long int, long long int>'} and 'int')
   14 |             a[i][0]=a[i-1][1]/2;
In file included from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127:
/usr/include/c++/14/complex:430:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator/(const complex<_Tp>&, const comple