poj2186——Popular Cows

今天重温tarjan算法。代码：

#include<iostream>#include<stdio.h>#include<stdlib.h>#include<stack>#include<string.h>using namespace std;#define N 10005#define min(a,b) (a<b? (a):(b))class node{public:int u,v,next;};node g[N*5];int len,head[N];int n,m;void add(int a,int b){g[++len].u =a;g[len].v =b;g[len].next =head[a];head[a]=len;}int low[N],dfn[N],index,belong[N],cnt,vis[N];stack<int >q;void tarjan(int u){int i;low[u]=dfn[u]=++index;q.push (u);vis[u]=1;for(i=head[u];i;i=g[i].next){int v=g[i].v ;if(!dfn[v]){tarjan(v);low[u]=min(low[u],low[v]);}else if(vis[v])low[u]=min(low[u],dfn[v]);}if(dfn[u]==low[u]){cnt++;int k;do{k=q.top ();belong[k]=cnt;q.pop ();vis[k]=0;}while(!q.empty ()&&k!=u);}}void find(){int i,ans,flag,k;memset(vis,1,sizeof(vis));for(i=1;i<=len;i++){if(belong[g[i].u ]!=belong[g[i].v ])vis[belong[g[i].u ]]=0;}flag=0;k=0;for(i=1;i<=cnt;i++)if(vis[i]){flag++;k=i;}if(flag>1)printf("%d\n",0);else{ans=0;for(i=1;i<=n;i++)if(belong[i]==k)ans++;printf("%d\n",ans);}}void solve(){memset(dfn,0,sizeof(dfn));memset(vis,0,sizeof(vis));index =0,cnt=0;for(int i=1;i<=n;i++){if(!dfn[i])tarjan(i);}find();}int main(){len =0;memset(head,0,sizeof(head));cin>>n>>m;for(int i=0;i<m;i++){int a,b;scanf("%d%d",&a,&b);add(a,b);}solve();return 0;}

悲剧，真是悲剧！太悲剧了~这是我想说的，这道题，就不知刷了多少提交次数了，一直RE，就是不见Accepted！悲剧！

tarjan算法没错，错的是a[],b[]数组开小了，好郁闷的说，调试了一天整有余了，才恍然大悟！

#include<stdio.h>#include<iostream>#include<stack>using namespace std;#include<string.h>#define max 10005typedef struct node{int to;node * next;};int dfn[max],low[max],belong[max];stack<int> st;bool instack[max];node * g[max];int n,m;int a[50005],b[50005];int index,top,bcnt;void tarjan(int i){int j,k;node * p;dfn[i]=low[i]=++index;instack[i]=true;st.push (i);p=g[i];while(p!=NULL){j=p->to ;if(!dfn[j]){tarjan(j);if(low[j]<low[i])low[i]=low[j];}else if(instack[j]&&dfn[j]<low[i])low[i]=dfn[j];p=p->next ;}if(dfn[i]==low[i]){bcnt++;do{k=st.top();st.pop ();instack[k]=false;belong[k]=bcnt;}while(i!=k);}}void solve(){int i;top=index=bcnt=0;memset(dfn,0,sizeof(dfn));memset(instack,false,sizeof(instack));memset(belong,0,sizeof(belong));for(i=1;i<=n;i++)if(!dfn[i])tarjan(i);}void find(){int vis[max];int i,ans,flag,k;memset(vis,1,sizeof(vis));for(i=0;i<m;i++){if(belong[a[i]]!=belong[b[i]])vis[belong[a[i]]]=0;}flag=0;k=0;for(i=1;i<=bcnt;i++)if(vis[i]){flag++;k=i;}if(flag>1)printf("%d/n",0);else{ans=0;for(i=1;i<=n;i++)if(belong[i]==k)ans++;printf("%d/n",ans);}}void add(int u,int v){node * p=new node;p->to =v;p->next =g[u];g[u]=p;}int main(){int i,x,y;node * p;scanf("%d%d",&n,&m);for(i=1;i<=n;i++)g[i]=NULL;for(i=0;i<m;i++){scanf("%d%d",&x,&y);a[i]=x;b[i]=y;add(x,y);}solve();find();return 0;}