【POJ3352】Road Construction（边双联通分量）

题意：给一个无向图，问最少添加多少条边后能使整个图变成双连通分量。

思路：双连通分量缩点，缩点后给度为1的分量两两之间连边，要连(ans+1) div 2条

low[u]即为u所在的分量编号，flag=0,1,2表示没搜过，没搜完，搜完了

POJ上pascal编译器出问题了不管怎么交都CE

这次写的 应该能处理重边

 var head,vet,next,flag,dfn,low,fan,de:array[..]of longint;
     n,m,i,e,v,ans,x,y,tot,time:longint;

 procedure add(a,b:longint);
 begin
  inc(tot);
  next[tot]:=head[a];
  vet[tot]:=b;
  head[a]:=tot;
 end;

 function min(x,y:longint):longint;
 begin
  if x<y then exit(x);
  exit(y);
 end;

 procedure dfs(u,le:longint);
 var e,v:longint;
 begin
  flag[u]:=;
  inc(time); dfn[u]:=time; low[u]:=time;
  e:=head[u];
  while e<> do
  begin
   v:=vet[e];
   if e=fan[le] then
   begin
    e:=next[e];
    continue;
   end;
   if flag[v]= then
   begin
    dfs(v,e);
    low[u]:=min(low[u],low[v]);
   end
    else if flag[v]= then low[u]:=min(low[u],dfn[v]);
   e:=next[e];
  end;
  flag[u]:=;
 end;

 begin

  for i:= to  do
    if i mod = then fan[i]:=i+
     else fan[i]:=i-;
  while not eof do
  begin
   readln(n,m);
   if (n=)and(m=) then break;
   fillchar(head,sizeof(head),);
   fillchar(low,sizeof(low),);
   fillchar(de,sizeof(de),);
   fillchar(flag,sizeof(flag),);
   tot:=; time:=;
   for i:= to m do
   begin
    read(x,y);
    add(x,y);
    add(y,x);
   end;
   for i:= to n do
    if flag[i]= then dfs(i,);
   for i:= to n do
   begin
    e:=head[i];
    while e<> do
    begin
     v:=vet[e];
     if low[v]<>low[i] then inc(de[low[i]]);
     e:=next[e];
    end;
   end;
   ans:=;
   for i:= to n do
    if de[i]= then inc(ans);
   writeln((ans+) div );
  end;

 end.

这个是去年写的那时候AC了 好像不能处理重边

 var de,low,next,vet,head,flag,dfn:array[..]of longint;
     n,m,tot,x,y,i,e,v,leaf,time:longint;

 function min(x,y:longint):longint;
 begin
  if x<y then exit(X);
  exit(y);
 end;

 procedure add(a,b:longint);
 begin
  inc(tot);
  next[tot]:=head[a];
  vet[tot]:=b;
  head[a]:=tot;
 end;

 procedure dfs(u,fa:longint);
 var e,v:longint;
 begin
  inc(time);
  dfn[u]:=time; low[u]:=time;
  flag[u]:=;
  e:=head[u];
  while e<> do
  begin
   v:=vet[e];
   if v=fa then
   begin
    e:=next[e];
    continue;
   end;
   if flag[v]= then
   begin
    dfs(v,u);
    low[u]:=min(low[u],low[v]);
   end
    else if flag[v]= then low[u]:=min(low[u],dfn[v]);
   e:=next[e];
  end;
  flag[u]:=;
 end;

 begin

  while not eof do
  begin
   readln(n,m);
   if (n=)and(m=) then break;
   fillchar(head,sizeof(head),);
   tot:=;
   for i:= to m do
   begin
    readln(x,y);
    add(x,y);
    add(y,x);
   end;
   fillchar(dfn,sizeof(dfn),);
   fillchar(de,sizeof(de),);
   fillchar(flag,sizeof(flag),);
   time:=;
   for i:= to n do
    if flag[i]= then dfs(i,i);
   for i:= to n do
   begin
    e:=head[i];
    while e<> do
    begin
     v:=vet[e];
     if low[i]<>low[v] then inc(de[low[i]]);
     e:=next[e];
    end;
   end;
   leaf:=;
   for i:= to n do
    if de[i]= then inc(leaf);
   writeln((leaf+) div );
  end;

 end.

UPD（2018.10.18）：C++

 #include<cstdio>
 #include<cstring>
 #include<string>
 #include<cmath>
 #include<iostream>
 #include<algorithm>
 #include<map>
 #include<set>
 #include<queue>
 #include<vector>
 using namespace std;
 typedef long long ll;
 typedef unsigned int uint;
 typedef unsigned long long ull;
 typedef pair<int,int> PII;
 typedef vector<int> VI;
 #define fi first
 #define se second
 #define MP make_pair
 #define N   15000
 #define M   6100000
 #define eps 1e-8
 #define pi  acos(-1)
 #define oo  1e9

 int head[N],vet[N],nxt[N],flag[N],dfn[N],low[N],fan[N],d[N],
     tot,tim;

 void add(int a,int b)
 {
     nxt[++tot]=head[a];
     vet[tot]=b;
     head[a]=tot;
 }

 void dfs(int u,int le)
 {
     flag[u]=;
     dfn[u]=low[u]=++tim;
     int e=head[u];
     while(e)
     {
         int v=vet[e];
         if(e==fan[le])
         {
             e=nxt[e];
             continue;
         }
         if(!flag[v])
         {
             dfs(v,e);
             low[u]=min(low[u],low[v]);
         }
          else if(flag[v]==) low[u]=min(low[u],dfn[v]);
         e=nxt[e];
     }
     flag[u]=;
 }

 int main()
 {
     freopen("poj3352.in","r",stdin);
     freopen("poj3352.out","w",stdout);
     for(int i=;i<=;i++)
      if(i&) fan[i]=i+;
       else fan[i]=i-;
     int n,m;
     while(scanf("%d%d",&n,&m)!=EOF)
     {
         memset(head,,sizeof(head));
         memset(low,,sizeof(low));
         memset(d,,sizeof(d));
         memset(flag,,sizeof(flag));
         tot=tim=;
         for(int i=;i<=m;i++)
         {
             int x,y;
             scanf("%d%d",&x,&y);
             add(x,y);
             add(y,x);
         }
         for(int i=;i<=n;i++)
          if(flag[i]==) dfs(i,);
         for(int i=;i<=n;i++)
         {
             int e=head[i];
             while(e)
             {
                 int v=vet[e];
                 if(low[v]!=low[i]) d[low[i]]++;
                 e=nxt[e];
             }
         }
         int ans=;
         for(int i=;i<=n;i++)
          if(d[i]==) ans++;
         printf("%d\n",(ans+)/);
     }
     return ;
 }