poj 1986（LCA tarjan算法）

题目：给一棵带权树，然后让你求任意两点之间的距离。

思路：tarjan一边dfs求出dis[i]每个点到根的距离，ans[i]第i组查询的lca。ans = dis[u]+dis[v]-2*dis[lca]。

代码如下：

/**************************************************
 * Author     : xiaohao Z
 * Blog     : http://www.cnblogs.com/shu-xiaohao/
 * Last modified : 2014-02-09 09:18
 * Filename     : hdu_2586.cpp
 * Description     : 
 * ************************************************/

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <queue>
#include <stack>
#include <vector>
#include <set>
#include <map>
#define MP(a, b) make_pair(a, b)
#define PB(a) push_back(a)

using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<unsigned int,unsigned int> puu;
typedef pair<int, double> pid;
typedef pair<ll, int> pli;
typedef pair<int, ll> pil;

const int INF = 0x3f3f3f3f;
const double eps = 1E-6;
const int LEN = 40000+10;
vector<pii> Map[LEN], que[LEN];
pii qv[LEN];
int n, m, q, vis[LEN], fa[LEN], ancestor[LEN], ans[LEN], dis[LEN];

void init(){
    for(int i=0; i<LEN; i++) {
        Map[i].clear();
        que[i].clear();
        fa[i] = i;     
    }
    memset(vis, 0, sizeof vis);
    memset(ancestor, 0, sizeof ancestor);
}
//UFSet
int Find(int x){return fa[x] == x ? x : fa[x] = Find(fa[x]);}
void Union(int a, int b){int pa = Find(a), pb = Find(b);if(pa != pb) fa[pa] = pb;}

void tarjan(int u){
    ancestor[u] = u;
    vis[u] = 1;
    for(int i=0; i<Map[u].size(); i++){
        int v = Map[u][i].first;
        if(vis[v]) continue;
        dis[v] = dis[u] + Map[u][i].second;
        tarjan(v);
        Union(u, v);
        ancestor[Find(u)] = u;
    }
    for(int i=0; i<que[u].size(); i++){
        int v = que[u][i].first, idx = que[u][i].second;
        if(vis[v])ans[idx] = ancestor[Find(v)];
    }
}

int main()
{
//    freopen("in.txt", "r", stdin);

    int a, b, val;
    char tc[10];
    while(scanf("%d%d", &n, &m)!=EOF){
        init();
        for(int i=0; i<m; i++) {
            scanf("%d%d%d", &a, &b, &val);
            gets(tc);
            Map[a].PB(MP(b, val));
            Map[b].PB(MP(a, val));
        }
        scanf("%d", &q);
        for(int i=0; i<q; i++){
            scanf("%d%d", &a, &b);
            qv[i] = MP(a, b);
            que[a].PB(MP(b, i));
            que[b].PB(MP(a, i));
        }
        dis[1] = 0;
        tarjan(1);
        for(int i=0; i<q; i++){
            printf("%d
", dis[qv[i].first]+dis[qv[i].second]-2*dis[ans[i]]);
        }
    }
    return 0;
}