View Compilation Error

0_0_31790485_28247.cpp:8:1: error: 'unordered_map' does not name a type
 unordered_map<int, int> mp;
 ^
0_0_31790485_28247.cpp: In function 'int solve(int)':
0_0_31790485_28247.cpp:14:8: error: 'mp' was not declared in this scope
     if(mp.count(x)) return 0;
        ^
0_0_31790485_28247.cpp:15:5: error: 'mp' was not declared in this scope
     mp[x] = 1;
     ^