HDU 2586 How far away ？ Tarjan 離線最近公共祖先

題目鏈接：http://acm.hdu.edu.cn/showproblem.php?pid=2586

裸的最近公共祖先

代碼：

#include <bits/stdc++.h>
#define sf scanf
#define pf printf

using namespace std;
const int maxn = 40000 + 50,maxnm = 200 + 5;
int fa[maxn],vis[maxn];
vector<int> Adj[maxn],Weight[maxn];
vector<int> NEXT_QUEARY[maxn],IDX[maxn];
int ans[maxn];
int Find(int a){
    return fa[a] == -1 ? a : fa[a] = Find(fa[a]);
}
void UNION(int a,int b){
    fa[Find(b)] = Find(a);
}
int dis[maxn];
void DFS(int u,int d){
    dis[u] = d;
    vis[u] = 1;int len = Adj[u].size(),v;
    for(int i = 0;i < len;++i){
        v = Adj[u][i];
        if(vis[v]) continue;
        DFS(v,d + Weight[u][i]);
        UNION(u,v);
    }
    len = NEXT_QUEARY[u].size();
    for(int i = 0;i < len;++i){
        if(vis[NEXT_QUEARY[u][i]])
            ans[IDX[u][i]] = dis[u] + dis[NEXT_QUEARY[u][i]] - 2 * dis[Find(NEXT_QUEARY[u][i])];
    }
}
void INIT(int n){
    memset(vis,0,sizeof vis);
    memset(fa,-1,sizeof fa);
    for(int i = 0;i <= n;++i) Adj[i].clear(),Weight[i].clear(),NEXT_QUEARY[i].clear(),IDX[i].clear();
}


int main(){
    int T;sf("%d",&T);
    while(T--){
        int n,m;sf("%d %d",&n,&m);
        INIT(n);
        for(int i = 0;i < n - 1;++i){
            int u,v,c;sf("%d %d %d",&u,&v,&c);
            Adj[u].push_back(v),Weight[u].push_back(c);
            Adj[v].push_back(u),Weight[v].push_back(c);
        }
        for(int i = 0;i < m;++i){
            int u,v;sf("%d %d",&u,&v);
            NEXT_QUEARY[u].push_back(v),IDX[u].push_back(i);
            NEXT_QUEARY[v].push_back(u),IDX[v].push_back(i);
        }
        DFS(1,0);
        for(int i = 0;i < m;++i) pf("%d\n",ans[i]);
    }
}