poj3177 tarjan缩点+割边 模板 【pascal】

1、tarjan缩点求割边

2、缩点后此时一定形成一棵树，再把割边加回来求缩点后的各个点的度

3、至少在树上添加(leaf+1)/2 条边,就能 使树达到边二连通,leaf的度为1

var        n,m,l,ans,a,b   :longint;        time,top,p,q    :longint;        vis             :array[0..10010] of boolean;        low,dfn,z,belong:array[0..5010] of longint;        indu            :array[0..10010] of longint;        last            :array[0..5010] of longint;        pre,other       :array[0..20010] of longint;        ge              :array[0..20010] of boolean;        i               :longint;procedure connect(x,y:longint);begin   inc(l);   pre[l]:=last[x];   last[x]:=l;   other[l]:=y;end;function min(a,b:longint):longint;begin   if a<b then exit(a) else exit(b);end;procedure dfs(x,father:longint);var        p,q,cur:Longint;begin   inc(time);   low[x]:=time;   dfn[x]:=time;   vis[x]:=true;   inc(top);   z[top]:=x;   //   q:=last[x];   while (q<>0) do   begin      p:=other[q];      if dfn[p]=0 then      begin         dfs(p,x);         low[x]:=min(low[x],low[p]);         if low[p]>dfn[x] then         begin            ge[q]:=true;            if (q mod 2=0) then ge[q-1]:=true             else ge[q+1]:=true;         end;      end else      if vis[p] and (p<>father) then low[x]:=min(low[x],dfn[p]);//      q:=pre[q];   end;   //   if (dfn[x]=low[x]) then   begin      cur:=-1;      while (cur<>x) do      begin         cur:=z[top];         dec(top);         vis[cur]:=false;         belong[cur]:=x+n;      end;   end;end;begin   read(n,m);l:=0;ans:=0;   for i:=1 to m do   begin      read(a,b);      connect(a,b);      connect(b,a);   end;   dfs(1,0);   //   fillchar(vis,sizeof(vis),false);   for i:=1 to n do   begin      q:=last[i];      while (q<>0) do      begin         if ge[q] then inc(indu[belong[i]]);         q:=pre[q];      end;   end;   //   fillchar(vis,sizeof(vis),false);   for i:=1 to n do    if (indu[belong[i]]=1) and not vis[belong[i]] then    begin       inc(ans);vis[belong[i]]:=true;    end;   //   ans:=(ans+1) div 2;   writeln(ans);end.

——by Eirlys