POJ1947 Rebuilding Roads

 1 /*by SilverN*/
 2 #include<algorithm>
 3 #include<iostream>
 4 #include<cstring>
 5 #include<cstdio>
 6 #include<cmath>
 7 #include<vector>
 8 using namespace std;
 9 const int mxn=160;
10 int read(){
11     int x=0,f=1;char ch=getchar();
12     while(ch<‘0‘ || ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
13     while(ch>=‘0‘ && ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
14     return x*f;
15 }
16 int n,p;
17 int f[mxn][mxn];
18 int num[mxn];
19 vector<int>e[mxn];
20 void dp(int u){
21     int i,j,k;
22     num[u]=1;
23     if(!e[u].size()){f[u][1]=0;return;}
24     for(i=0;i<e[u].size();i++){
25         int v=e[u][i];
26         dp(v);
27         num[u]+=num[v];
28         for(j=num[u];j;j--){
29             for(k=1;k<j;k++){
30                 f[u][j]=min(f[u][j],f[u][j-k]+f[v][k]-1);
31             }
32         }
33     }
34     return;
35 }
36 int main(){
37     n=read();p=read();
38     int i,j;
39     int u,v;
40     for(i=1;i<n;i++){
41         u=read();v=read();
42         e[u].push_back(v);
43         num[u]++;
44     }
45     memset(f,0x3f,sizeof f);
46     for(i=1;i<=n;i++){
47         f[i][1]=num[i];
48     }
49     dp(1);
50     int ans=f[1][p];
51     for(i=1;i<=n;i++){
52         ans=min(ans,f[i][p]+1);
53     }
54     printf("%d\n",ans);
55     return 0;
56 }