View Compilation Error

0_0_8959336_30125.cpp: In function `void solve(int)':
0_0_8959336_30125.cpp:22: error: no match for 'operator!=' in 'x != (&st)->std::set<_Key, _Compare, _Alloc>::end [with _Key = int, _Compare = std::less<int>, _Alloc = std::allocator<int>]()'