View Compilation Error

0_0_16448092_30081.cpp: In function 'void solve()':
0_0_16448092_30081.cpp:30:46: error: 'class std::queue<int>' has no member named 'push_back'
     for(i = 0; i < n; ++i) if(f[a[i]]==-1) q.push_back(a[i]),f[a[i]] = 0;
                                              ^