Luogu1041 NOIP2003传染病控制（搜索）

　　暴搜加个最优性剪枝即可。一直觉得正式比赛出这种不能一眼看出来暴搜就行了的搜索题的出题人都是毒瘤。

#include<iostream> 
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
int read()
{
    int x=0,f=1;char c=getchar();
    while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
    while (c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
    return x*f;
}
#define N 310
int n,p[N],deep[N],a[N][N],ans=N,fa[N],t,m;
bool flag[N];
struct data{int to,nxt;
}edge[N<<1];
void addedge(int x,int y){t++;edge[t].to=y,edge[t].nxt=p[x],p[x]=t;}
void dfs(int k)
{
    a[deep[k]][++a[deep[k]][0]]=k;m=max(m,deep[k]);
    for (int i=p[k];i;i=edge[i].nxt)
    if (edge[i].to!=fa[k])
    {
        deep[edge[i].to]=deep[k]+1;
        fa[edge[i].to]=k;
        dfs(edge[i].to);
    }
}
void paint(int k,bool color)
{
    flag[k]=color;
    for (int i=p[k];i;i=edge[i].nxt)
    if (edge[i].to!=fa[k]) paint(edge[i].to,color);
}
void cut(int k,int cnt)
{
    int t=cnt;
    for (int i=1;i<=a[k][0];i++)
    if (!flag[a[k][i]]) cnt++;
    if (cnt>=ans) return;
    if (k==m) {ans=min(ans,cnt);return;}
    for (int i=1;i<=a[k][0];i++)
    if (!flag[a[k][i]])
        for (int j=p[a[k][i]];j;j=edge[j].nxt)
        if (edge[j].to!=fa[a[k][i]])
        {
            paint(edge[j].to,1);
            cut(k+1,cnt);
            paint(edge[j].to,0);
        }
    cut(k+1,cnt);
    cnt=t;
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("1041.in","r",stdin);
    freopen("1041.out","w",stdout);
    const char LL[]="%I64d
";
#else
    const char LL[]="%lld
";
#endif
    n=read();read();
    for (int i=1;i<n;i++)
    {
        int x=read(),y=read();
        addedge(x,y),addedge(y,x);
    }
    dfs(1);
    cut(0,0);
    cout<<ans;
    return 0;
}