foo.cc: In function ‘int main(int, char**)’:
foo.cc:8:5: error: ‘vector’ was not declared in this scope
    8 |     vector<pair<int,int>> arr(n+1);
      |     ^~~~~~
foo.cc:3:1: note: ‘std::vector’ is defined in header ‘<vector>’; did you forget to ‘#include <vector>’?
    2 | #include <algorithm>
  +++ |+#include <vector>
    3 | using namespace std;
foo.cc:8:24: error: expected primary-expression before ‘>’ token
    8 |     vector<pair<int,int>> arr(n+1);
      |                        ^~
foo.cc:8:27: error: ‘arr’ was not declared in this scope
    8 |     vector<pair<int,int>> arr(n+1);
      |                           ^~~