View Compilation Error

0_0_37619101_9888.cpp: In function 'void solve()':
0_0_37619101_9888.cpp:15:5: error: 'unordered_map' was not declared in this scope
     unordered_map<char, int> st;
     ^
0_0_37619101_9888.cpp:15:19: error: expected primary-expression before 'char'
     unordered_map<char, int> st;
                   ^
0_0_37619101_9888.cpp:22:13: error: 'st' was not declared in this scope
         if (st[s[j]] == 0)  cnt++;
             ^
0_0_37619101_9888.cpp:23:9: error: 'st' was not declared in this scope
         st[s[j]]++;
         ^