poj 1330 Nearest Common Ancestors（離線LCA）

題目鏈接：http://poj.org/problem?id=1330

題意：T組樣例，n-1條邊，1次詢問，求最近公共祖先。

#include<iostream>
#include<cstdio>
#include<vector>
using namespace std;

const int INF=0x3f3f3f3f;
const int maxn=10010;
int T,n;
int degree[maxn],vis[maxn];
int ancestor[maxn];

vector<int>tree[maxn];
vector<int>query[maxn];

int f[maxn],r[maxn];

void Make_Set(){
	for(int i=0;i<=n;i++){
		f[i]=i;
		r[i]=1;
	}
}

int find(int x){
	return x==f[x]?x:f[x]=find(f[x]);
}

void Union(int a,int b){
	int ra=find(a);
	int rb=find(b);
	if(ra==rb) return ;
	if(r[ra]>r[rb]){
		f[rb]=ra;
		r[ra]+=r[rb];
	}
	else{
		f[ra]=rb;
		r[rb]+=r[ra];
	}
}

void Tarjan(int root){
	for(int i=0;i<tree[root].size();i++){
		if(!vis[tree[root][i]]){
			Tarjan(tree[root][i]);
			Union(root,tree[root][i]);
			ancestor[find(root)]=root;
		}
	}
	vis[root]=1;
	for(int i=0;i<query[root].size();i++){
		if(vis[query[root][i]]){
			printf("%d\n",ancestor[find(query[root][i])]);
		}
	}
}

void Init(){
	Make_Set();
	memset(vis,0,sizeof(vis));
	memset(degree,0,sizeof(degree));
	for(int i=0;i<=n;i++){
		tree[i].clear();
		query[i].clear();
		ancestor[i]=i;
	}
}

int main(){
#ifndef ONLINE_JUDGE
	freopen("test.in","r",stdin);
	freopen("test.out","w",stdout);
#endif
	scanf("%d",&T);
	while(T--){
		scanf("%d",&n);
		Init();
		int x,y;
		for(int i=0;i<n-1;i++){
			scanf("%d%d",&x,&y);
			tree[x].push_back(y);
			degree[y]++;
		}
		scanf("%d%d",&x,&y);
		query[x].push_back(y);
		query[y].push_back(x);
		int root;
		for(int i=1;i<=n;i++){
			if(!degree[i]){
				root=i;
				break;
			}
		}
		Tarjan(root);
	}
	return 0;
}