View Compilation Error

0_0_37843139_12983.cpp: In function 'void solve()':
0_0_37843139_12983.cpp:88:43: error: 'first' was not declared in this scope
     for(int i=1;i<=n;++i) edge[i].clear(),first[i]=0,scanf("%d",&a[i]),pos[a[i]]=i;
                                           ^