NOIP2015信息传递

来源：互联网发布：紫色水离子淘宝店名字编辑：程序博客网时间：2024/05/29 19:58

Tarjan求最小生成环（注意要形成一个环而不是一个点，即size>1），这真的很模板...

var        n,x,l,time,top,t,minn:longint;        i                    :longint;        dfn,low,z,size       :array[0..200010] of longint;        last,pre,other       :array[0..200010] of longint;        vis                  :array[0..200010] of boolean;function min(a,b:longint):longint;begin   if a<b then exit(a) else exit(b);end;procedure connect(x,y:longint);begin   inc(l);   pre[l]:=last[x];   last[x]:=l;   other[l]:=y;end;procedure dfs(x: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);         low[x]:=min(low[x],low[p]);      end else      if vis[p] then low[x]:=min(low[x],dfn[p]);      q:=pre[q];   end;   //   if (dfn[x]=low[x]) then   begin      cur:=-1;inc(t);      while (cur<>x) do      begin         cur:=z[top];         dec(top);         vis[cur]:=false;         inc(size[t]);      end;   end;end;begin   read(n);   for i:=1 to n do   begin      read(x);      connect(i,x);   end;   //   for i:=1 to n do if (dfn[i]=0) then dfs(i);   minn:=maxlongint;   for i:=1 to t do    if (size[i]<minn) and (size[i]>1) then minn:=size[i];   writeln(minn);end.

——by Eirlys
转载请注明出处=w=

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