Language: C++

#include <bits/stdc++.h>

typedef long long ll;

using namespace std;

int main() {
    int n;
    cin >> n;
    vector<vector<int>> tree(n + 1);
    for (int i = 0; i < n - 1; i++) {
        int a, b;
        cin >> a >> b;
        tree[a].emplace_back(b);
        tree[b].emplace_back(a);
    }
    set<pair<int, int>> threes;
    for (int i = 1; i <= n; i++) {
        queue<tuple<int, int, vector<bool>>> q;
        vector<bool> reached(n + 1, false);
        q.push(make_tuple(i, 0, reached));
        while(!q.empty()) {
            auto f = q.front();
            q.pop();
            if (f < 3) {
                int idx = get<0>(f);
                reached[idx] = true;
                for (int& e: tree[idx]) {
                    if (!get<2>(f)[e]) {
                        q.push(make_tuple(e, get<1>(f) + 1, reached));
                    }
                }
            } else {
                int v = get<0>(f);
                if (i > v) {
                    threes.insert(make_pair(v, i));
                } else {
                    threes.insert(make_pair(i, v));
                }
            }
        }
    }
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:25:19: error: no match for 'operator<' (operand types are 'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' and 'int')
   25 |             if (f < 3) {
      |                 ~ ^ ~
      |                 |   |
      |                 |   int
      |                 std::tuple<int, int, std::vector<bool, std::allocator<bool> > >
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:1143:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1143 |     operator<(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1143:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/bits/regex.h:1224:5: 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>&)'
 1224 |     operator<(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1224:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/bits/regex.h:1317:5: 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>&)'
 1317 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1317:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/bits/regex.h:1391:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1391 |     operator<(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1391:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/bits/regex.h:1485:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1485 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1485:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/bits/regex.h:1560:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1560 |     operator<(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1560:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/bits/regex.h:1660:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1660 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1660:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   25 |             if (f < 3) {
      |                     ^
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:1045:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator<(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1045 |     operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1045:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'const std::pair<_T1, _T2>'
   25 |             if (f < 3) {
      |                     ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:448:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  448 |     operator<(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:448:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'const std::reverse_iterator<_Iterator>'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/bits/stl_iterator.h:493:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  493 |     operator<(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'const std::reverse_iterator<_Iterator>'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1694 |     operator<(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'const std::move_iterator<_IteratorL>'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1760 |     operator<(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'const std::move_iterator<_IteratorL>'
   25 |             if (f < 3) {
      |                     ^
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/string_view:673:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  673 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:673:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/string_view:680:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  680 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:680:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   'std::tuple<int, int, std::vector<bool, std::allocator<bool> > >' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/string_view:688:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  688 |     operator< (__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:688:5: note:   template argument deduction/substitution failed:
a.cc:25:21: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'int'
   25 |             if (f < 3) {
      |                     ^
/usr/include/c++/14/bits/basic_string.h:3874:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3874 |     operator<(const basic_string<_CharT, _Traits, _Al