http://poj.org/problem?id=3352
1 #include <cstdio> 2 #include <iostream> 3 #include <cstring> 4 #include <queue> 5 #include <algorithm> 6 #define maxn 300000 7 using namespace std; 8 9 const int inf=1<<30; 10 int head[maxn],dfn[maxn],low[maxn],belong[maxn],stack1[maxn],du[maxn]; 11 int e,bcc_clock,bcnt,top,N,E; 12 bool vis[maxn],visi[maxn]; 13 14 struct node 15 { 16 int u,v,next; 17 } p[maxn]; 18 19 void add(int u,int v) 20 { 21 p[e].u=u; 22 p[e].v=v; 23 p[e].next=head[u]; 24 head[u]=e++; 25 p[e].u=v; 26 p[e].v=u; 27 p[e].next=head[v]; 28 head[v]=e++; 29 } 30 31 void tarjan(int u,int fa) 32 { 33 vis[u]=true; 34 dfn[u]=low[u]=++bcc_clock; 35 stack1[++top]=u; 36 for(int i=head[u]; i!=-1; i=p[i].next) 37 { 38 int v=p[i].v; 39 if(v==fa) continue; 40 if(!dfn[v]) 41 { 42 tarjan(v,u); 43 low[u]=min(low[u],low[v]); 44 } 45 else if(vis[v]) 46 { 47 low[u]=min(low[u],dfn[v]); 48 } 49 } 50 if(dfn[u]==low[u]) 51 { 52 bcnt++; 53 int j; 54 do 55 { 56 j=stack1[top--]; 57 vis[j]=false; 58 belong[j]=bcnt; 59 } 60 while(j!=u); 61 } 62 } 63 64 void deal() 65 { 66 bcc_clock=0,bcnt=0,top=0; 67 memset(vis,false,sizeof(vis)); 68 memset(belong,0,sizeof(belong)); 69 memset(dfn,0,sizeof(dfn)); 70 tarjan(1,1); 71 } 72 73 void dfs(int u) 74 { 75 visi[u]=true; 76 for(int i=head[u]; i!=-1; i=p[i].next) 77 { 78 int v=p[i].v; 79 if(!visi[v]) 80 { 81 if(belong[v]!=belong[u]) 82 { 83 ++du[belong[u]]; 84 ++du[belong[v]]; 85 } 86 dfs(v); 87 } 88 } 89 } 90 void inti() 91 { 92 memset(head,-1,sizeof(head)); 93 e=0; 94 } 95 96 int main() 97 { 98 while(cin>>N>>E) 99 { 100 inti(); 101 int x,y; 102 for(int i=0; i<E; i++) 103 { 104 scanf("%d%d",&x,&y); 105 add(x,y); 106 } 107 deal(); 108 if(bcnt==1) 109 { 110 printf("0 "); 111 continue; 112 } 113 memset(du,0,sizeof(du)); 114 int leaf=0; 115 memset(visi,false,sizeof(visi)); 116 dfs(1); 117 for(int i=1; i<=bcnt; i++) 118 { 119 if(du[i]==1) leaf++; 120 } 121 printf("%d ",(leaf+1)/2); 122 } 123 return 0; 124 }