poj 1144 (tju 1026)

Description
ATelephone Line Company (TLC) is establishing a new telephone cable network.They are connecting several places numbered by integers from 1 to N . No twoplaces have the same number. The lines are bidirectional and
always connecttogether two places and in each place the lines end in a telephone exchange.There is one telephone exchange in each place. From each place it is 

possible to reach through lines every other place, however it need not be adirect connection, it can go through several exchanges. From time to time thepower supply fails at a place and then the exchange does not operate. Theofficials from TLC realized that
in such a case it can happen that besides thefact that the place with the failure is unreachable, this can also cause thatsome other places cannot connect to each other. In such a case we will say theplace (where the failure 

occured) is critical. Now the officials are trying to write a program forfinding the number of all such critical places. Help them.
Input
The inputfile consists of several blocks of lines. Each block describes one network. Inthe first line of each block there is the number of places N < 100. Each ofthe next at most N lines contains the number of a
place followed by the numbersof some places to which there is a direct line from this place. These at most Nlines completely describe the network, i.e., each direct connection of twoplaces in the network is contained at least in one row. All numbers in one
lineare separated 

by one space. Each block ends with a line containing just 0. The last block hasonly one line with N = 0;
Output
The outputcontains for each block except the last in the input file one line containingthe number of critical places.
Sample Input（简析）
5            （5个点）
5 1 2 3 4 （5号点与1，2，3，4有双向边，后面有若干个数）
0             （每组数据以0结束）
6
2 1 3
5 4 6 2
0
0         （输入以一个0结束）
Sample Output
1
2
Hint
You needto determine the end of one line.In order to make it's easy to determine,thereare no extra blank before the end of each line.
 

分析：求图的割点数目。

 

const

 maxn=1000;

 maxv=20000;

type

 node=record

 y,other,next:longint;

 f:boolean;

end;

 

var

 g:array [1..maxv] of node;

 dfn,low,ls:array [1..maxn] of longint;

 b:array [1..maxn] of boolean;

 n,p,e,v:longint;

procedure add(x,y:longint);

 begin

 inc(e);

 g[e].y:=y;

 g[e].other:=e+1;

 g[e].next:=ls[x];

 ls[x]:=e;

 inc(e);

 g[e].y:=x;

 g[e].other:=e-1;

 g[e].next:=ls[y];

 ls[y]:=e;

 end;

 

function min(x,y:longint):longint;

begin

 if x<y then exit(x)

       else exit(y);

end;

 

procedure dfs(x:longint);

 var

 t:longint;

begin

 inc(p);

 dfn[x]:=p;

 low[x]:=p;

 t:=ls[x];

 while t>0 do

 with g[t] do

  begin

   if not f then

    begin

     f:=true;

     g[other].f:=true;

     if dfn[y]=0 then

      begin

       if x=1 then inc(v);

       dfs(y);

       low[x]:=min(low[x],low[y]);

       if low[y]>=dfn[x] then b[x]:=true;

      end

      else

       low[x]:=min(low[x],dfn[y]);

    end;

   t:=next;

  end;

end;

 

procedure tarjan;

 begin

 dfs(1);

  if v>1 then b[1]:=true else b[1]:=false;

 end;

 

procedure print;

 var i,ans:longint;

begin

 ans:=0;

 for i:=1 to n do

  if b[i] then inc(ans);

 writeln(ans);

end;

 

procedure init;

var

 x,y:longint;

begin

 repeat

 fillchar(ls,sizeof(ls),0);

 e:=0; p:=0; v:=0;

 fillchar(g,sizeof(g),0);

 fillchar(dfn,sizeof(dfn),0);

 fillchar(low,sizeof(low),0);

 fillchar(b,sizeof(b),false);

 readln(n);

  if n=0 then break;

  repeat

   read(x);

   if x=0 then break;

   while not eoln do

    begin

     read(y);

     add(x,y);

    end;

  until false;

 tarjan;

 print;

 until false;

end;

 

 

begin

 init;

end.