HDU ACM 1269 迷宫城堡 (Tarjan,DFS)
http://acm.hdu.edu.cn/showproblem.php?pid=1269
思路:Tarjan算法,模版题
1 #include <iostream> 2 #include <vector> 3 #include <stack> 4 using namespace std; 5 const int MAX = 10000 + 10; 6 int n; 7 vector <int> v[MAX]; 8 stack <int> s; 9 int mark_stack[MAX]; 10 int dfn[MAX]; 11 int low[MAX]; 12 int time; 13 int sum; 14 void Tarjan(int rank){ 15 dfn[rank] = low[rank] = ++time; 16 s.push(rank); 17 mark_stack[rank] = 1; 18 int i; 19 for(i=0;i<v[rank].size();i++){ 20 if(!dfn[v[rank][i]]){ 21 Tarjan(v[rank][i]); 22 low[rank] = min(low[rank],low[v[rank][i]]); 23 } 24 else{ 25 if(mark_stack[v[rank][i]]){ 26 low[rank] = min(low[rank],dfn[v[rank][i]]); 27 } 28 } 29 } 30 if(low[rank] == dfn[rank]){ 31 sum++; 32 int x = s.top(); 33 mark_stack[x] = 0; 34 s.pop(); 35 while(x != rank){ 36 x = s.top(); 37 mark_stack[x] = 0; 38 s.pop(); 39 } 40 } 41 42 } 43 int main(){ 44 int m; 45 while(cin>>n>>m,n+m){ 46 while(!s.empty()){ 47 s.pop(); 48 } 49 int i; 50 for(i=0;i<MAX;i++){ 51 v[i].clear(); 52 } 53 memset(dfn,0,sizeof(dfn)); 54 memset(low,0,sizeof(low)); 55 memset(mark_stack,0,sizeof(mark_stack)); 56 while(m--){ 57 int x,y; 58 cin>>x>>y; 59 v[x].push_back(y); 60 } 61 sum = 0; 62 time = 0; 63 for(i=1;i<=n;i++){ 64 if(!dfn[i]){ 65 if(sum){ 66 sum++; 67 break; 68 } 69 else{ 70 Tarjan(1); 71 } 72 } 73 74 } 75 if(sum == 1){ 76 cout<<"Yes"<<endl; 77 } 78 else{ 79 cout<<"No"<<endl; 80 } 81 } 82 return 0; 83 }
