Hdu--3594（仙人掌图）

2014-11-01 18:56:51、

思路：判断仙人掌图，具体看：https://files.cnblogs.com/ambition/cactus_solution.pdf

　　主要是判断3个性质：（1）没有横向边（2）没有桥（3）每个点u及其子节点v中返回u的祖先节点的边数和<2

 1 /*************************************************************************
 2     > File Name: 3594.cpp
 3     > Author: Nature
 4     > Mail: 564374850@qq.com 
 5     > Created Time: Sat 01 Nov 2014 05:33:01 PM CST
 6 ************************************************************************/
 7 
 8 #include <cstdio>
 9 #include <cstring>
10 #include <cstdlib>
11 #include <cmath>
12 #include <vector>
13 #include <map>
14 #include <set>
15 #include <stack>
16 #include <queue>
17 #include <iostream>
18 #include <algorithm>
19 using namespace std;
20 #define lp (p << 1)
21 #define rp (p << 1|1)
22 #define getmid(l,r) (l + (r - l) / 2)
23 #define MP(a,b) make_pair(a,b)
24 typedef long long ll;
25 const int INF = 1 << 30;
26 const int maxn = 20010;
27 
28 int T,n;
29 int first[maxn],next[50010],ver[50010],ecnt;
30 int dfn[maxn],low[maxn],vis[maxn],tot;
31 
32 void Init(){
33     memset(first,-1,sizeof(first));
34     ecnt = 0;
35 }
36 
37 void Add_edge(int u,int v){
38     next[++ecnt] = first[u];
39     ver[ecnt] = v;
40     first[u] = ecnt;
41 }
42 
43 bool Dfs(int p){
44     dfn[p] = low[p] = ++tot;
45     vis[p] = 1;
46     int ac = 0,bc = 0;
47     for(int i = first[p]; i != -1; i = next[i]){
48         int v = ver[i];
49         if(vis[v] == 2) return false;
50         if(!dfn[v]){
51             if(!Dfs(v)) return false;
52             if(low[v] > dfn[p]) return false;
53             if(low[v] < dfn[p]) ++ac;
54             low[p] = min(low[p],low[v]);
55         }
56         else if(dfn[v] < dfn[p]){
57             low[p] = min(low[p],dfn[v]);
58             ++bc;
59         }
60     }
61     vis[p] = 2;
62     if(ac + bc >= 2) return false;
63     return true;
64 }
65 
66 bool Tarjan(){
67     memset(dfn,0,sizeof(dfn));
68     memset(low,0,sizeof(low));
69     memset(vis,0,sizeof(vis));
70     tot = 0;
71     for(int i = 1; i <= n; ++i) if(!dfn[i])
72         if(!Dfs(i)) return false;
73     return true;
74 }
75 
76 int main(){
77     int a,b;
78     scanf("%d",&T);
79     while(T--){
80         Init();
81         scanf("%d",&n);
82         while(scanf("%d%d",&a,&b) != EOF && (a || b)){
83             Add_edge(a,b);
84         }
85         if(Tarjan()) printf("YES\n");
86         else printf("NO\n");
87     }
88     return 0;
89 }

 

posted @ 2014-11-01 18:59  Naturain  阅读(179)  评论(0)  编辑  收藏  举报