[NOIP2003] 传染病控制 搜索+剪枝

#include <cstdio>
#include <vector>
#include <algorithm>
#define MAXN 310
namespace pre{
  inline void read(int &sum){
    register char ch=getchar();
    for(sum=0;ch<‘0‘||ch>‘9‘;ch=getchar());
    for(;ch>=‘0‘&&ch<=‘9‘;sum=(sum<<1)+(sum<<3)+ch-‘0‘,ch=getchar());
  }
  inline int Max(int x,int y){
    return x>y?x:y;
  }
  int ans;
}
namespace tree{
  struct tree{
    int to,next;
  }c[MAXN<<1];
  int head[MAXN],t,size[MAXN],f[MAXN],Deep_Max,Max[MAXN];
  bool did[MAXN];
  std::vector<int> floor[MAXN];
  inline int comp(int x,int y){
    return size[x]>size[y];
  }
  inline void add(int x,int y){
    c[++t].to=y;
    c[t].next=head[x];
    head[x]=t;
  }
  inline void dfs(int x,int fa,int deep){
    Deep_Max=pre::Max(deep,Deep_Max);
    size[x]=1;
    f[x]=fa;
    floor[deep].push_back(x);
    for(int i=head[x];i;i=c[i].next)
      if(c[i].to!=fa)
        dfs(c[i].to,x,deep+1),size[x]+=size[c[i].to];
  }
  inline void Dfs(int deep,int ans){
    //if(ans+Max[deep+1]<=pre::ans)return;
    pre::ans=pre::Max(ans,pre::ans);
    if(deep==Deep_Max)return;
    for(int i=0;i<floor[deep+1].size();i++)
      if(did[f[floor[deep+1][i]]])
        did[floor[deep+1][i]]=1;
    for(int i=0;i<floor[deep+1].size();i++)
      if(did[floor[deep+1][i]]==0){
        did[floor[deep+1][i]]=1;
        Dfs(deep+1,ans+size[floor[deep+1][i]]);
        did[floor[deep+1][i]]=0;
      }
    for(int i=0;i<floor[deep+1].size();i++)
      if(did[f[floor[deep+1][i]]])
        did[floor[deep+1][i]]=0;
  }
}
namespace mid{
  int n,m;
  inline void Init(){
    using pre :: read;
    using tree :: add;
    read(n),read(m);
    for(int i=1,a,b;i<=m;i++)
      read(a),read(b),add(a,b),add(b,a);
    tree :: dfs(1,0,1);
  }
  inline void Work(){
    using namespace tree;
    for(int i=Deep_Max;i>1;i--){
      std::sort(floor[i].begin(),floor[i].end(),comp);
      Max[i]=Max[i+1]+size[floor[i][0]];
    }
    Dfs(1,0);
    printf("%d",n-pre::ans);
  }
}
int main(){
  freopen("epidemic.in","r",stdin);
  freopen("epidemic.out","w",stdout);
  mid :: Init();
  mid :: Work();
  return 0;
}