View Compilation Error

0_0_39654462_12139.cpp: In function 'void union_(long long int, long long int)':
0_0_39654462_12139.cpp:31:20: error: cannot bind non-const lvalue reference of type 'long long int&' to an rvalue of type 'long long int'
   31 |     auto& ri = root(i), rj = root(j);
      |                ~~~~^~~