View Compilation Error

0_0_37465419_18525.cpp:15:5: error: 'set' does not name a type
     set <int> s;
     ^
0_0_37465419_18525.cpp: In function 'int main()':
0_0_37465419_18525.cpp:28:21: error: 'struct node' has no member named 's'
     no[i].a=0,no[i].s.clear();
                     ^
0_0_37465419_18525.cpp:33:11: error: 'struct node' has no member named 's'
     no[x].s.insert(y);
           ^
0_0_37465419_18525.cpp:34:11: error: 'struct node' has no member named 's'
     no[y].s.insert(x);
           ^
0_0_37465419_18525.cpp:56:15: error: 'struct node' has no member named 's'
     j=*(no[i].s.begin());
               ^
0_0_37465419_18525.cpp:57:11: error: 'struct node' has no member named 's'
     no[j].s.erase(i);
           ^