【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[0..10000]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]:=1;
 inc(time); dfn[u]:=time; low[u]:=time;
 e:=head[u];
 while e<>0 do
 begin
  v:=vet[e];
  if e=fan[le] then
  begin
   e:=next[e];
   continue;
  end;
  if flag[v]=0 then
  begin
   dfs(v,e);
   low[u]:=min(low[u],low[v]);
  end
   else if flag[v]=1 then low[u]:=min(low[u],dfn[v]);
  e:=next[e];
 end;
 flag[u]:=2;
end;

begin

 for i:=0 to 2000 do
   if i mod 2=1 then fan[i]:=i+1
    else fan[i]:=i-1;
 while not eof do
 begin
  readln(n,m);
  if (n=0)and(m=0) then break;
  fillchar(head,sizeof(head),0);
  fillchar(low,sizeof(low),0);
  fillchar(de,sizeof(de),0);
  fillchar(flag,sizeof(flag),0);
  tot:=0; time:=0;
  for i:=1 to m do
  begin
   read(x,y);
   add(x,y);
   add(y,x);
  end;
  for i:=1 to n do
   if flag[i]=0 then dfs(i,0);
  for i:=1 to n do
  begin
   e:=head[i];
   while e<>0 do
   begin
    v:=vet[e];
    if low[v]<>low[i] then inc(de[low[i]]);
    e:=next[e];
   end;
  end;
  ans:=0;
  for i:=1 to n do
   if de[i]=1 then inc(ans);
  writeln((ans+1) div 2);
 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[1..10000]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]:=1;
 e:=head[u];
 while e<>0 do
 begin
  v:=vet[e];
  if v=fa then
  begin
   e:=next[e];
   continue;
  end;
  if flag[v]=0 then
  begin
   dfs(v,u);
   low[u]:=min(low[u],low[v]);
  end
   else if flag[v]=1 then low[u]:=min(low[u],dfn[v]);
  e:=next[e];
 end;
 flag[u]:=2;
end;

begin

 while not eof do
 begin
  readln(n,m);
  if (n=0)and(m=0) then break;
  fillchar(head,sizeof(head),0);
  tot:=0;
  for i:=1 to m do
  begin
   readln(x,y);
   add(x,y);
   add(y,x);
  end;
  fillchar(dfn,sizeof(dfn),0);
  fillchar(de,sizeof(de),0);
  fillchar(flag,sizeof(flag),0);
  time:=0;
  for i:=1 to n do
   if flag[i]=0 then dfs(i,i);
  for i:=1 to n do
  begin
   e:=head[i];
   while e<>0 do
   begin
    v:=vet[e];
    if low[i]<>low[v] then inc(de[low[i]]);
    e:=next[e];
   end;
  end;
  leaf:=0;
  for i:=1 to n do
   if de[i]=1 then inc(leaf);
  writeln((leaf+1) div 2);
 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]=1;
    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]==1) low[u]=min(low[u],dfn[v]);
        e=nxt[e];
    }
    flag[u]=2;
}

int main()
{
    freopen("poj3352.in","r",stdin);
    freopen("poj3352.out","w",stdout);
    for(int i=0;i<=2000;i++) 
     if(i&1) fan[i]=i+1;
      else fan[i]=i-1;
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        memset(head,0,sizeof(head));
        memset(low,0,sizeof(low));
        memset(d,0,sizeof(d));
        memset(flag,0,sizeof(flag));
        tot=tim=0;
        for(int i=1;i<=m;i++)
        {
            int x,y;
            scanf("%d%d",&x,&y);
            add(x,y);
            add(y,x);
        }
        for(int i=1;i<=n;i++)
         if(flag[i]==0) dfs(i,0);
        for(int i=1;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=0;
        for(int i=1;i<=n;i++)
         if(d[i]==1) ans++;
        printf("%d\n",(ans+1)/2); 
    }
    return 0;
}