SP14932 LCA - Lowest Common Ancestor

#include<bits/stdc++.h>
using namespace std;
const int maxn=1e6+7;
struct node1{
    int nxt;
    int to;
}tree[maxn*2];
struct node2{
    int nxt;
    int to;
    int LCA;
}qtree[maxn*2];
int head1[maxn],cnt1;
void add1(int x,int y){
    tree[++cnt1].nxt=head1[x];
    tree[cnt1].to=y;
    head1[x]=cnt1;
}
int head2[maxn],cnt2;
void add2(int x,int y){
    qtree[++cnt2].nxt=head2[x];
    qtree[cnt2].to=y;
    head2[x]=cnt2;
}
int vis[maxn];
int fa[maxn];
int fifa(int x){
    if(x!=fa[x]) return fa[x]=fifa(fa[x]);
}
void Tarjan(int x){
    vis[x]=1;
    for(int i=head1[x];i;i=tree[i].nxt){
        int v=tree[i].to;
        if(vis[v]) continue;
        Tarjan(v);
        fa[v]=x;
    }
    for(int i=head2[x];i;i=qtree[i].nxt){
        int v=qtree[i].to;
        if(vis[v]){
            qtree[i].LCA=fifa(v);
            if(i%2){
                qtree[i+1].LCA=qtree[i].LCA;
            }
            else qtree[i-1].LCA=qtree[i].LCA;
        }
    }
}
int T,ljb,n,m,k,x,y;
int main(){
    scanf("%d",&T);
    while(T--){
        ljb++;
        scanf("%d",&n);
        memset(head1,0,sizeof(head1));
        memset(head2,0,sizeof(head2));
        cnt1=0,cnt2=0;
        memset(qtree,0,sizeof(qtree));
        memset(tree,0,sizeof(tree));
        memset(vis,0,sizeof(vis));
        for(int i=1;i<=n;i++) fa[i]=i;
        for(int i=1;i<=n;i++){
            scanf("%d",&m);
            for(int j=1;j<=m;j++){
                scanf("%d",&x);
                add1(x,i);
                add1(i,x);
            }
        }
        scanf("%d",&k);
        for(int i=1;i<=k;i++){
            scanf("%d%d",&x,&y);
            add2(x,y);
            add2(y,x);
        }
        Tarjan(1);
        printf("Case %d:\n",ljb);
        for(int i=1;i<=k;i++){
            printf("%d\n",qtree[i*2].LCA);
        }
    }
    return 0;
}

Tarjan seeking LCA, fight really cool