Language: C++

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


vector<pair<int,int>> gra;
ll dist[10050];

void dfs(ll x,ll y){
  for(const auto& it:gra[x]){
    ll s=it.first,len=it.second;
    if(dist[s])continue;
    dist[s]=y+len;
    dfs(s,dist[s]);
  }
}

int main(){
  int n,q,k;cin >> n;
  gra.resize(n-1);
  rep(i,n-1){
    int a,b,c;cin >> a>>b>>c;
    a--;b--;
    gra[a].pb(b,c);
    gra[b].pb(a,c);
  }
  cin >> q>>k;
  k--;
  dfs(k,0);
  rep(i,q){
    int x,y;cin >> x>>y;x--;y--;
    ll ans=dist[x]+dist[y];
    cout << ans << endl;
  }
}
  

Compiler output:
a.cc: In function 'void dfs(ll, ll)':
a.cc:11:27: error: no matching function for call to 'begin(std::pair<int, int>&)'
   11 |   for(const auto& it:gra[x]){
      |                           ^
In file included from /usr/include/c++/14/bits/algorithmfwd.h:39,
                 from /usr/include/c++/14/bits/stl_algo.h:59,
                 from /usr/include/c++/14/algorithm:61,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/initializer_list:88:5: note: candidate: 'template<class _Tp> constexpr const _Tp* std::begin(initializer_list<_Tp>)'
   88 |     begin(initializer_list<_Tp> __ils) noexcept
      |     ^~~~~
/usr/include/c++/14/initializer_list:88:5: note:   template argument deduction/substitution failed:
a.cc:11:27: note:   'std::pair<int, int>' is not derived from 'std::initializer_list<_Tp>'
   11 |   for(const auto& it:gra[x]){
      |                           ^
In file included from /usr/include/c++/14/string:53,
                 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/range_access.h:52:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&)'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:52:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&) [with _Container = std::pair<int, int>]':
a.cc:11:27:   required from here
   11 |   for(const auto& it:gra[x]){
      |                           ^
/usr/include/c++/14/bits/range_access.h:52:50: error: 'struct std::pair<int, int>' has no member named 'begin'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |                                           ~~~~~~~^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&)'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&) [with _Container = std::pair<int, int>]':
a.cc:11:27:   required from here
   11 |   for(const auto& it:gra[x]){
      |                           ^
/usr/include/c++/14/bits/range_access.h:63:56: error: 'const struct std::pair<int, int>' has no member named 'begin'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |                                                 ~~~~~~~^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note: candidate: 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::begin(_Tp (&)[_Nm])'
   95 |     begin(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note:   template argument deduction/substitution failed:
a.cc:11:27: note:   mismatched types '_Tp [_Nm]' and 'std::pair<int, int>'
   11 |   for(const auto& it:gra[x]){
      |                           ^
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166:
/usr/include/c++/14/valarray:1227:5: note: candidate: 'template<class _Tp> _Tp* std::begin(valarray<_Tp>&)'
 1227 |     begin(valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1227:5: note:   template argument deduction/substitution failed:
a.cc:11:27: note:   'std::pair<int, int>' is not derived from 'std::valarray<_Tp>'
   11 |   for(const auto& it:gra[x]){
      |                           ^
/usr/include/c++/14/valarray:1238:5: note: candidate: 'template<class _Tp> const _Tp* std::begin(const valarray<_Tp>&)'
 1238 |     begin(const valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1238:5: note:   template argument deduction/substitution failed:
a.cc:11:27: note:   'std::pair<int, int>' is not derived from 'const std::valarray<_Tp>'
   11 |   for(const auto& it:gra[x]){
      |                           ^
a.cc:11:27: error: no matching function for call to 'end(std::pair<int, int>&)'
/usr/include/c++/14/initializer_list:99:5: note: candidate: 'template<class _Tp> constexpr const _Tp* std::end(initializer_list<_Tp>)'
   99 |     end(initializer_list<_Tp> __ils) noexcept
      |     ^~~
/usr/include/c++/14/initializer_list:99:5: note:   template argument deduction/substitution failed:
a.cc:11:27: note:   'std::pair<int, int>' is not derived from 'std::initializer_list<_Tp>'
   11 |   for(const auto& it:gra[x]){
      |                           ^
/usr/include/c++/14/bits/range_access.h:74:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.end()) std::end(_Container&)'
   74 |     end(_Container& __cont) -> decltype(__cont.end())
      |     ^~~
/usr/include/c++/14/bits/range_access.h:74:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.end()) std::end(_Container&) [with _Container = std::pair<int, int>]':
a.cc:11:27:   required from here
   11 |   for(const auto& it:gra[x]){
      |                           ^
/usr/include/c++/14/bits/range_access.h:74:48: error: 'struct std::pair<int, int>' has no member named 'end'
   74 |     end(_Container& __cont) -> decltype(__cont.end())
      |                                         ~~~~~~~^~~
/usr/include/c++/14/bits/range_access.h:85:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.end()) std::end(const _Container&)'
   85 |     end(const _Container& __cont) -> decltype(__cont.end())
      |     ^~~
/usr/include/c++/14/bits/range_access.h:85:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.end()) std::end(const _Container&) [with _Container = std::pair<int, int>]':
a.cc:11:27:   required from here
   11 |   for(const auto& it:gra[x]){
      |                           ^
/usr/include/c++/14/bits/range_access.h:85:54: error: 'const struct std::pair<int, int>' has no member named 'end'
   85 |     end(const _Container& __cont) -> decltype(__cont.end())
      |                                               ~~~~~~~^~~
/usr/include/c++/14/bits/range_access.h:106:5: note: candidate: 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::end(_Tp (&)[_Nm])'
  106 |     end(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~
/usr/include/c++/14/bits/range_access.h:106:5: note:   template argument deduction/substitution failed:
a.cc:11:27: note:   mismatched types '_Tp [_Nm]' and 'std::pair<int, int>'
   11 |   for(const auto& it:gra[x]){
      |                           ^
/usr/include/c++/14/valarray:1249:5: note: candidate: 'template<class _Tp> _Tp* std::end(valarray<_Tp>&)'
 1249 |     end(valarray<_Tp>& __va) noexcept
      |     ^~~
/usr/include/c++/14/valarray:1249:5: note:   template argument deduction/substitution failed:
a.cc:11:27: note:   'std::pair<int, int>' is not derived from 'std::valarray<_Tp>'
   11 |   for(const auto& it:gra[x]){
      |                           ^
/usr/include/c++/14/valarray:1265:5: note: candidate: 'template<class _Tp> const _Tp* std::end(const valarray<_Tp>&)'
 1265 |     end(const valarray<_Tp>& __va) noexcept
      |     ^~~
/usr/include/c++/14/valarray:1265:5: note:   template argument deduction/substitution failed:
a.cc:11:27: note:   'std::pair<int, int>' is not derived from 'const std::valarray<_Tp>'
   11 |   for(const auto& it:gra[x]){
      |                           ^
a.cc:14:15: error: 'len' was not declared in this scope
   14 |     dist[s]=y+len;
      |               ^~~
a.cc: In function 'int main()':
a.cc:25:12: error: '__gnu_cxx::__alloc_traits<std::allocator<std::pair<int, int> >, std::pair<int, int> >::value_type' {aka 'struct std::pair<int, int>'} has no member named 'pb'
   25 |     gra[a].pb(b,c);
      |            ^~
a.cc:26:12: error: '__gnu_cxx::__alloc_traits<std::allocator<std::pair<int, int> >, std::pair<int, int> >::value_type' {aka 'struct std::pair<int, int>'} has no member named 'pb'
   26 |     gra[b].pb(a,c);
      |            ^~