foo.cc: In function ‘int main()’:
foo.cc:21:63: error: ‘pow’ was not declared in this scope
   21 |                 if (left)  x = f[left - 1][right] + a[left] * pow(2, dep);
      |                                                               ^~~
foo.cc:23:72: error: ‘pow’ was not declared in this scope
   23 |                 if (right) y = f[left][right - 1] + a[m - right + 1] * pow(2, dep);
      |                                                                        ^~~