View Compilation Error

0_0_36949318_5512.cpp: In function 'void solve()':
0_0_36949318_5512.cpp:27:13: error: no match for 'operator!' (operand type is 'std::map<long long int, int>::iterator {aka std::_Rb_tree_iterator<std::pair<const long long int, int> >}')
         if (!mp.find(s[i]))
             ^
0_0_36949318_5512.cpp:27:13: note: candidate is:
0_0_36949318_5512.cpp:27:13: note: operator!(bool) <built-in>
0_0_36949318_5512.cpp:27:13: note:   no known conversion for argument 1 from 'std::map<long long int, int>::iterator {aka std::_Rb_tree_iterator<std::pair<const long long int, int> >}' to 'bool'