题目：poj 1470 Closest Common Ancestors

题意：给出一个树，一些询问。求LCA的个数、

分析：很简单的模板题目，但是模板不够优秀，一直wa...RE，各种错误一下午，终于发现自己模板的漏洞了。

AC代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
using namespace std;
#define N 1010
#define M 20010

struct Node
{
    int to,val;
};
vector<Node> g[N];
struct ask{
    int u,v,lca;
};
vector<ask> e;
vector<int> query[N];
int fa[N],ance[N],dir[N];
bool vis[N];

inline void add_Node(int u ,int v,int w)
{
    g[u].push_back((Node){v,w});
    g[v].push_back((Node){u,w});
}

inline void add_ask(int u ,int v )
{
    e.push_back((ask){u,v,-1});
    e.push_back((ask){v,u,-1});
    int len = e.size()-1;
    query[v].push_back(len);
    query[u].push_back(len-1);
}

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

void Tarjan(int u,int val)
{
    vis[u] = true;
    ance[u] = fa[u] = u;
    dir[u] = val;
    for(int i=0;i<g[u].size();i++)
    {
        Node tmp = g[u][i];
        if(!vis[tmp.to])
        {
            Tarjan(tmp.to,val+tmp.val);
            fa[tmp.to] = u;
        }
    }
    for(int i=0;i<query[u].size();i++)
    {
        int num = query[u][i];
        ask& tmp = e[num];
        if(vis[tmp.v])
        {
            tmp.lca = e[num^1].lca = ance[find(tmp.v)];
        }
    }
}
int ans[N],flag[N];
void Clear(int n)
{
    memset(vis,false,sizeof(vis));
    memset(ans,0,sizeof(ans));
    memset(flag,0,sizeof(flag));
    for(int i=0;i<=n;i++){
        g[i].clear();
        query[i].clear();
    }
    e.clear();
}
int main()
{
    //freopen("Input.txt","r",stdin);
    int n;
    int u,x,m;
    char ch;
    while(scanf("%d",&n)!=EOF)
    {
        Clear(n);
        for(int i=1;i<=n;i++)
        {
            scanf("%d:(%d)",&u,&m);
            while(m--)
            {
                scanf("%d",&x);
                flag[x]=true;
                add_Node(x,u,1);
            }
        }
        int Q;
        scanf("%d",&Q);
        for(int i=1;i<=Q;i++)
        {
            cin>>ch;
            scanf("%d%d",&u,&x);
            cin>>ch;
            add_ask(u,x);
        }
        int root;
        for(int i=1;i<=n;i++)
          if(!flag[i])
          {
              root=i;
              break;
          }
        Tarjan(root,0);
        for(int i = 0;i< Q;i++)
        {
            ans[e[i*2].lca]++;
        }
        for(int i = 1; i<= N;i++)
        {
            if(ans[i])
                printf("%d:%d\n",i,ans[i]);
        }
    }
    return 0;
}

poj 1470 Closest Common Ancestors 【Tarjan 离线 LCA】