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1 //10180085 perseawe 2186 accepted 1424k 79ms pascal 2645b 2012-05-10
19:54:27
23 var
4 n,m,tot,numofblocks,time,top:longint;
5 dfn,low,hv,faim,stack:array [0..10000+100] of longint;
6 vis,instack:array [0..10000+100] of boolean;
7 edge:array [0..50000+500] of record wh,next:longint;end;
89 procedure addedge(u,v:longint);
10begin
11 inc(tot);
12 edge[tot].next:=hv[u];hv[u]:=tot;
13 edge[tot].wh:=v;
14end;
1516 procedure init;
17var
18 i,u,v:longint;
19begin
20 readln(n,m);
21 tot:=0;fillchar(hv,sizeof(hv),0);
22for i:=1
to m do
23begin
24 readln(u,v);
25 addedge(u,v);
26end;
27end;
2829 function min(a,b:longint):longint;begin
if athen exit(a);exit(b);end;
3031 procedure tarjan(u:longint);
32var
33 v,tnode:longint;
34begin
35 inc(time);
36 dfn[u]:=time;low[u]:=time;vis[u]:=true;
37 inc(top);stack[top]:=u;instack[u]:=true;
38 tnode:=hv[u];
39while tnode<>0
do40
begin
41 v:=edge[tnode].wh;
42if
not(vis[v]) then//樹枝邊,min取low
43begin
44 tarjan(v);
45 low[u]:=min(low[u],low[v]);
46end
47else
48if instack[u] then low[u]:=min(low[u],dfn[v]);//後向弧，low和dfn
49 tnode:=edge[tnode].next;
50end;
51if dfn[u]=low[u] then//找到乙個分支，下面是彈棧+標記的過程
52begin
53 inc(numofblocks);
54 repeat
55 v:=stack[top];
56 faim[v]:=numofblocks;
57 instack[v]:=false;
58 dec(top);
59 until u=v;
60end;
61end;
6263 procedure main;
64var i:longint;
6566
begin
67 fillchar(vis,sizeof(vis),false);
68 fillchar(instack,sizeof(instack),false);
69 fillchar(dfn,sizeof(dfn),0);
7071 top:=0;numofblocks:=0;
72 for i:=1
to n do
73if not(vis[i]) then
74 tarjan(i);
7576 for i:=1
to n do writeln(i,'
aim to
',faim[i]);
7778
79end;
8081 procedure print;
82var
83 i,tmp,ans,u,v,tnode:longint;
84begin
85 fillchar(dfn,sizeof(dfn),0);
86 for i:=1
to n do
87begin
88 tnode:=hv[i];u:=faim[i];
89 while tnode<>0
do90
begin
91 v:=faim[edge[tnode].wh];
92if u<>v then inc(dfn[u]);//如果不在乙個強連通分治中
93 tnode:=edge[tnode].next;
94end;
95end;
96 tmp:=0;
97 for i:=1
to numofblocks do
98if dfn[i]=0
then
begin inc(tmp);ans:=i;end;
99if tmp>1
then
begin writeln(0);halt;end;
100 tmp:=ans;ans:=0;
101 for i:=1
to n do
if faim[i]=tmp then inc(ans);
102 writeln(ans);
103end;
104105 begin
106107 assign(input,'
p2186.in
');reset(input);
108 //assign(output,'
p2186.out
');rewrite(output);
109110
111 init;
112 main;
113 print;
114115
116 close(input);close(output);
117118 end.
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