poj 1330 Nearest Common Ancestors （最简单的LCA）

int const maxn = 10005;

int T,n,a,b;
int fa[maxn];
int X,Y;

int main(){
    cin>>T;
    while(T--){
        scanf("%d",&n);
        mem(fa,-1);
        rep(i,1,n-1){
            scanf("%d%d",&a,&b);
            fa[b]=a;
        }
        scanf("%d%d",&X,&Y);
        map<int,char> mp;
        int t1=X;
        while(t1!=-1){
            mp[t1]=1;
            t1=fa[t1];
        }
        t1=Y;
        while(t1!=-1){
            if(mp[t1]==1){
                printf("%d\n",t1);
                break;
            }
            t1=fa[t1];
        }
    }
}

int const maxn = 10005;

struct node{
    int to,w,next,lca;
};
node edge[maxn*2];

bool vis[maxn];
int cnt1,cnt2;
int head[maxn], fa[maxn];
bool flag;
int X,Y,n;

inline void Addedge(int u,int v,int w){
    edge[++cnt1].w=w;
    edge[cnt1].to=v;
    edge[cnt1].next=head[u];
    head[u]=cnt1;
}

void init(){
    mem(head,-1);
    mem(vis,false);
    cnt1=0;
    flag=false;
    rep(i,1,n) fa[i]=i;
}

int findFa(int x){
    if(fa[x]==x) return fa[x];
    return fa[x]=findFa(fa[x]);
}
void Tarjan_LCA(int u){ //离线LCA算法
    if(flag)
        return;
    fa[u]=u;
    vis[u]=true;
    for(int i=head[u];i!=-1;i=edge[i].next){
        if(!vis[edge[i].to]){
            Tarjan_LCA(edge[i].to);
            fa[edge[i].to]=u;
        }
    }
    if(u==Y && !flag){
        if(vis[X]){
            printf("%d\n",findFa(X));
            flag=true;
            return;
        }
    }
    if(u==X && !flag){
        if(vis[Y]){
            printf("%d\n",findFa(Y));
            flag=true;
            return;
        }
    }
}


int T,a,b;

int main(){
    cin>>T;
    while(T--){
        scanf("%d",&n);
        init();
        bool t1[maxn]={0};
        rep(i,1,n-1){
            scanf("%d%d",&a,&b);
            Addedge(a,b,1);
            t1[b]=true;
        }
        scanf("%d%d",&X,&Y);
        rep(i,1,n) if(!t1[i]){
            Tarjan_LCA(i); //i为树的根结点
            break;
        }
    }
}