HDU 1629 迷宫城堡

1 #include <iostream>
2 #include <cstdio>
3 #include <cstring>
4 #include <cstdlib>
5 #include <vector>
6 #include <algorithm>
7 using namespace std;
8
9 const int MAXN=100010;
10 const int MAXM=2000010;
11
12 struct Edge{
13     int to,next;
14 }edges[MAXM];
15 int head[MAXN],tot;
16
17 void init(){
18     memset(head,-1,sizeof(head));
19     tot=0;
20 }
21
22 void addEdge(int u,int v){
23     edges[tot].to=v;
24     edges[tot].next=head[u];
25     head[u]=tot++;
26 }
27
28 int DFN[MAXN],LOW[MAXN],Belong[MAXN],Stack[MAXN];
29 int Index,top;
30 int scc;
31 bool Instack[MAXN];
32 int num[MAXN];
33
34 void Tarjan(int u){
35     int v;
36     LOW[u]=DFN[u]=++Index;
37     Stack[top++]=u;
38     Instack[u]=true;
39
40     for(int i=head[u];i!=-1;i=edges[i].next){
41         v=edges[i].to;
42
43         if(!DFN[v]){
44             Tarjan(v);
45             if(LOW[u]>LOW[v]) LOW[u]=LOW[v];
46         }else if(Instack[v]&&LOW[u]>DFN[v])
47             LOW[u]=DFN[v];
48     }
49
50     if(LOW[u]==DFN[u]){
51         scc++;
52
53         do{
54             v=Stack[--top];
55             Instack[v]=false;
56             num[scc]++;
57             Belong[v]=scc;
58         }while(v!=u);
59     }
60 }
61
62 void solve(int N){
63     memset(DFN,0,sizeof(DFN));
64     memset(Instack,false,sizeof(Instack));
65     memset(num,0,sizeof(num));
66
67     Index=top=scc=0;
68
69     for(int i=1;i<=N;i++){
70         if(!DFN[i])
71             Tarjan(i);
72     }
73
74     if(scc>1)
75         cout<<"No"<<endl;
76     else
77         cout<<"Yes"<<endl;
78 }
79
80 int main(){
81     int n,m;
82     while(scanf("%d%d",&n,&m)!=EOF&&(n!=0||m!=0)){
83             init();
84         for(int i=0;i<m;i++){
85             int u,v;
86             scanf("%d%d",&u,&v);
87             addEdge(u,v);
88         }
89         solve(n);
90     }
91
92 }