foo.cpp: In function 'int main()':
foo.cpp:34:42: error: 'memset' was not declared in this scope
           memset(first1,-1,sizeof(first1));
                                          ^
foo.cpp:29:15: warning: unused variable 'j' [-Wunused-variable]
        long i,j,k,head,tail,x,pos;
               ^