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：

 1 /**************************************************
 2  * Author     : xiaohao Z
 3  * Blog     : http://www.cnblogs.com/shu-xiaohao/
 4  * Last modified : 2014-02-09 09:18
 5  * Filename     : hdu_2586.cpp
 6  * Description     : 
 7  * ************************************************/
 8 
 9 #include <iostream>
10 #include <cstdio>
11 #include <cstring>
12 #include <cstdlib>
13 #include <cmath>
14 #include <algorithm>
15 #include <queue>
16 #include <stack>
17 #include <vector>
18 #include <set>
19 #include <map>
20 #define MP(a, b) make_pair(a, b)
21 #define PB(a) push_back(a)
22 
23 using namespace std;
24 typedef long long ll;
25 typedef pair<int, int> pii;
26 typedef pair<unsigned int,unsigned int> puu;
27 typedef pair<int, double> pid;
28 typedef pair<ll, int> pli;
29 typedef pair<int, ll> pil;
30 
31 const int INF = 0x3f3f3f3f;
32 const double eps = 1E-6;
33 const int LEN = 40000+10;
34 vector<pii> Map[LEN], que[LEN];
35 pii qv[LEN];
36 int n, m, q, vis[LEN], fa[LEN], ancestor[LEN], ans[LEN], dis[LEN];
37 
38 void init(){
39     for(int i=0; i<LEN; i++) {
40         Map[i].clear();
41         que[i].clear();
42         fa[i] = i;     
43     }
44     memset(vis, 0, sizeof vis);
45     memset(ancestor, 0, sizeof ancestor);
46 }
47 //UFSet
48 int Find(int x){return fa[x] == x ? x : fa[x] = Find(fa[x]);}
49 void Union(int a, int b){int pa = Find(a), pb = Find(b);if(pa != pb) fa[pa] = pb;}
50 
51 void tarjan(int u){
52     ancestor[u] = u;
53     vis[u] = 1;
54     for(int i=0; i<Map[u].size(); i++){
55         int v = Map[u][i].first;
56         if(vis[v]) continue;
57         dis[v] = dis[u] + Map[u][i].second;
58         tarjan(v);
59         Union(u, v);
60         ancestor[Find(u)] = u;
61     }
62     for(int i=0; i<que[u].size(); i++){
63         int v = que[u][i].first, idx = que[u][i].second;
64         if(vis[v])ans[idx] = ancestor[Find(v)];
65     }
66 }
67 
68 int main()
69 {
70 //    freopen("in.txt", "r", stdin);
71 
72     int a, b, val;
73     char tc[10];
74     while(scanf("%d%d", &n, &m)!=EOF){
75         init();
76         for(int i=0; i<m; i++) {
77             scanf("%d%d%d", &a, &b, &val);
78             gets(tc);
79             Map[a].PB(MP(b, val));
80             Map[b].PB(MP(a, val));
81         }
82         scanf("%d", &q);
83         for(int i=0; i<q; i++){
84             scanf("%d%d", &a, &b);
85             qv[i] = MP(a, b);
86             que[a].PB(MP(b, i));
87             que[b].PB(MP(a, i));
88         }
89         dis[1] = 0;
90         tarjan(1);
91         for(int i=0; i<q; i++){
92             printf("%d\n", dis[qv[i].first]+dis[qv[i].second]-2*dis[ans[i]]);
93         }
94     }
95     return 0;
96 }
View Code

 

posted @ 2014-02-09 12:05  张小豪  阅读(351)  评论(0)  编辑  收藏  举报