/in/foo.cc: In member function 'int Splay::splay(int, int)':
/in/foo.cc:75:2: warning: no return statement in function returning non-void [-Wreturn-type]
  }
  ^
/in/foo.cc: In member function 'int Splay::build(int, int)':
/in/foo.cc:81:8: warning: operation on '((Splay*)this)->Splay::sz' may be undefined [-Wsequence-point]
    val[++sz] = w[sz] = s[l];
        ^~~~