View Compilation Error

0_0_38248969_32542.cpp:36:5: error: 'unordered_map' does not name a type
     unordered_map<ULL,int>book;
     ^
0_0_38248969_32542.cpp: In member function 'void StringHash::init()':
0_0_38248969_32542.cpp:39:9: error: 'book' was not declared in this scope
         book.clear(); return ;
         ^
0_0_38248969_32542.cpp: In member function 'int StringHash::insert(ULL, int)':
0_0_38248969_32542.cpp:43:13: error: 'book' was not declared in this scope
         if (book[val])
             ^
0_0_38248969_32542.cpp:49:9: error: 'book' was not declared in this scope
         book[val] = id;
         ^