In file included from /usr/include/c++/14/unordered_map:37,
                 from answer.code:4:
/usr/include/c++/14/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
   32 | #error This file requires compiler and library support \
      |  ^~~~~
answer.code: In member function ‘size_t KeyHash::operator()(const Key&) const’:
answer.code:23:16: error: ‘hash’ was not declared in this scope
   23 |         return hash<int>()(key.start) ^ hash<int>()(key.current_sum);
      |                ^~~~
answer.code:23:16: note: ‘std::hash’ is only available from C++11 onwards
answer.code:23:21: error: expected primary-expression before ‘int’
   23 |         return hash<int>()(key.start) ^ hash<int>()(key.current_sum);
      |                     ^~~
answer.code:23:21: error: expected ‘;’ before ‘int’
answer.code:23:24: error: expected unqualified-id before ‘>’ token
   23 |         return hash<int>()(key.start) ^ hash<int>()(key.current_sum);
      |                        ^
answer.code: At global scope:
answer.code:27:18: error: ‘>>’ should be ‘> >’ within a nested template argument list
   27 | vector<vector<int>> backtrack(int start, int current_sum, const vector<pair<int, int>> &menu_costs_with_indices, int target, unordered_map<Key, vector<vector<int>>, KeyHash> &memo) {
      |                  ^~
      |                  > >
answer.code:27:85: error: ‘>>’ should be ‘> >’ within a nested template argument list
   27 | vector<vector<int>> backtrack(int start, int current_sum, const vector<pair<int, int>> &menu_costs_with_indices, int target, unordered_map<Key, vector<vector<int>>, KeyHash> &memo) {
      |                                                                                     ^~
      |                                                                                     > >
answer.code:27:126: error: ‘unordered_map’ has not been declared
   27 | vector<vector<int>> backtrack(int start, int current_sum, const vector<pair<int, int>> &menu_costs_with_indices, int target, unordered_map<Key, vector<vector<int>>, KeyHash> &memo) {
      |                                                                                                                              ^~~~~~~~~~~~~
answer.code:27:139: error: expected ‘,’ or ‘...’ before ‘<’ token
   27 | vector<vector<int>> backtrack(int start, int current_sum, const vector<pair<int, int>> &menu_costs_with_indices, int target, unordered_map<Key, vector<vector<int>>, KeyHash> &memo) {
      |                                                                                                                                           ^
answer.code: In function ‘std::vector<std::vector<int> > backtrack(int, int, const std::vector<std::pair<int, int> >&, int, int)’:
answer.code:29:16: warning: extended initializer lists only available with ‘-std=c++11’ or ‘-std=gnu++11’ [-Wc++11-extensions]
   29 |         return {{}};
      |                ^
answer.code:29:19: warning: extended initializer lists only available with ‘-std=c++11’ or ‘-std=gnu++11’ [-Wc++11-extensions]
   29 |         return {{}};
      |                   ^
answer.code:29:19: warning: extended initializer lists only available with ‘-std=c++11’ or ‘-std=gnu++11’ [-Wc++11-extensions]
answer.code:32:16: warning: extended initializer lists only available with ‘-std=c++11’ or ‘-std=gnu++11’ [-Wc++11-extensions]
   32 |         return {};
      |                ^
answer.code:35:9: error: ‘memo’ was not declared in this scope
   35 |     if (memo.find(memo_key) != memo.end()) {
      |         ^~~~
answer.code:39:22: error: ‘>>’ should be ‘> >’ within a nested template argument list
   39 |     vector<vector<int>> combinations;
      |                      ^~
      |                      > >
answer.code:46:14: error: ‘sub_combinations’ does not name a type
   46 |         auto sub_combinations = backtrack(i, current_sum + cost, menu_costs_with_indices, target, memo);
      |              ^~~~~~~~~~~~~~~~
answer.code:47:20: error: ISO C++ forbids declaration of ‘comb’ with no type [-fpermissive]
   47 |         for (auto &comb : sub_combinations) {
      |                    ^~~~
answer.code:47:27: warning: range-based ‘for’ loops only available with ‘-std=c++11’ or ‘-std=gnu++11’ [-Wc++11-extensions]
   47 |         for (auto &comb : sub_combinations) {
      |                           ^~~~~~~~~~~~~~~~
answer.code:47:27: error: ‘sub_combinations’ was not declared in this scope; did you mean ‘combinations’?
   47 |         for (auto &comb : sub_combinations) {
      |                           ^~~~~~~~~~~~~~~~
      |                           combinations
answer.code:48:18: error: request for member ‘insert’ in ‘comb’, which is of non-class type ‘int’
   48 |             comb.insert(comb.begin(), index);
      |                  ^~~~~~
answer.code:48:30: error: r...