# "cf659e" New reform

Source: Internet
Author: User

Given the N and m two-way edges, change the bidirectional edge to one-way edge, and ask the minimum number of unreachable vertices?

Analysis:

If you cannot reach it, the entry level is 0.
DFS determines whether a ring exists in each of the connected blocks, and if there is a ring, it guarantees that each point in the ring has a degree greater than or equal to 1. Otherwise, the symbolizing, the head of the penetration is 0.

`1 varHead,vet,next,flag:Array[1..200000] ofLongint;2 N,m,x,y,tmp,ans,tot,i:longint;3 4 procedureAdd (a,b:longint);5 begin6 Inc (TOT);7next[tot]:=Head[a];8vet[tot]:=b;9head[a]:=tot;Ten End; One  A procedureDFS (u,pre:longint); - varE,v:longint; - begin the  ifflag[u]=1  Then begintmp:=0; ExitEnd; -flag[u]:=1; -e:=Head[u]; -   whileE<>0  Do +  begin -v:=Vet[e]; +   ifV<>pre ThenDFS (v,u); Ae:=Next[e]; at  End; - End; -  - begin -Assign (input,'1.in'); Reset (input); -Assign (output,'1.out'); Rewrite (output); in readln (n,m); -   fori:=1  toM Do to  begin + read (x, y); - Add (x, y); the Add (y,x); *  End; \$   fori:=1  toN DoPanax Notoginseng   ifflag[i]=0  Then -   begin thetmp:=1; +DFS (I,0); Aans:=ans+tmp; the   End; + writeln (ans); -//close (input); \$//close (output); \$ End.`
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"cf659e" New reform

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