View Compilation Error

0_0_18093380_5471.cpp:32:1: error: 'unordered_map' does not name a type
 unordered_map<double,int> M;
 ^
0_0_18093380_5471.cpp: In function 'LL solve1()':
0_0_18093380_5471.cpp:43:9: error: 'M' was not declared in this scope
         M.clear();
         ^