View Compilation Error

0_0_36404507_2290.cpp:27:1: error: 'unordered_map' does not name a type
 unordered_map<int,int>cnt;
 ^
0_0_36404507_2290.cpp: In function 'void init()':
0_0_36404507_2290.cpp:33:2: error: 'cnt' was not declared in this scope
  cnt.clear();
  ^
0_0_36404507_2290.cpp: In function 'void dfs(int, int)':
0_0_36404507_2290.cpp:51:6: error: 'cnt' was not declared in this scope
  if(!cnt[c[now]]) sum++;
      ^
0_0_36404507_2290.cpp:52:2: error: 'cnt' was not declared in this scope
  cnt[c[now]]++;
  ^