LCA 离线算法 Tarjan

转载一篇博客：http://www.cnblogs.com/ylfdrib/archive/2010/11/03/1867901.html

Tarjan实现: dfs + 并查集;

通过这道题体会一下把：(思路详见上面的博客)

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

#include<map>
#include<set>
#include<list>
#include<cmath>
#include<ctime>
#include<queue>
#include<stack>
#include<cctype>
#include<cstdio>
#include<string>
#include<vector>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#define MAXN 40005
using namespace std;

struct P
{
    int v, w;
};
struct Q
{
    int v, id;
};
vector <P> g[MAXN];        //存树
vector <Q> q[MAXN];        //存询问点对(u, v)

int dist[MAXN];            //dist[i]:根到i的距离
int vis[MAXN];    
int f[MAXN];            //并查集
int query[MAXN][3];        //存询问结果[u, v, lca(u,v)]

int find(int x){
    if(x != f[x])
        f[x] = find(f[x]);
    return f[x];
}

void add_g(int u, int v, int w){
    P t;
    t.v=v, t.w=w;
    g[u].push_back(t);
}

void add_q(int u, int v, int id){
    Q t;
    t.v=v, t.id=id;
    q[u].push_back(t);
}

void getDist(int u){
    vis[u] = 1;
    for(int i=0; i<g[u].size(); i++){
        int v = g[u][i].v,  w= g[u][i].w;
        if(!vis[v]){
            dist[v] = dist[u] + w;
            getDist(v);
        }
    }
}

void Tarjan(int u){
    vis[u] = 1;
    f[u] = u;    //!!
    for(int i=0; i<q[u].size(); i++){
        int v = q[u][i].v, id = q[u][i].id;
        if(vis[v])
            query[id][2] = find(v);
    }
    for(int i=0; i<g[u].size(); i++){
        int v = g[u][i].v,  w= g[u][i].w; 
        if(!vis[v]){
            Tarjan(v);
            f[v] = u;
        }
    }    
}

int main()
{    
    //hdu 2586
    int t;
    cin >> t;
    while(t--){
        int n, m;
        cin >> n >> m;
        for(int i=1; i<=n-1; i++){
            int u, v, w;
            scanf("%d%d%d", &u, &v, &w);
            add_g(u, v, w);
            add_g(v, u, w);
        }
        for(int i=1; i<=m; i++){
            int u, v;
            scanf("%d%d", &u, &v);
            query[i][0] = u;
            query[i][1] = v;
            add_q(u, v, i);
            add_q(v, u, i);
        }
        memset(vis, 0, sizeof(vis));
        dist[1] = 0;
        getDist(1);        //取1为根
        memset(vis, 0, sizeof(vis));
        Tarjan(1);
        for(int i=1; i<=m; i++){
            int u = query[i][0], v = query[i][1],
                lca = query[i][2];
            printf("%d
", dist[u]+dist[v]-2*dist[lca]);
        }
        for(int i=1; i<=n; i++){
            g[i].clear();
            q[i].clear();
        }
    }
    return 0;
}