树上的最大独立集

过程详见入门经典第二版280页，粘代码跑QAQ

 1 #include "iostream"
 2 #include "cstdio"
 3 #include "cstring"
 4 #include "string"
 5 #include "vector"
 6 using namespace std;
 7 const int maxn=1000+10;
 8 int n;
 9 vector<int> g[maxn];
10 int son[maxn],gson[maxn];
11 int f[maxn],dp[maxn],wide[maxn];
12 int wide_max;
13 void init(){
14     scanf("%d",&n);
15     for(int i=1;i<n;i++){
16         int x,y;
17         scanf("%d%d",&x,&y);
18         g[x].push_back(y);
19         g[y].push_back(x);
20     }
21 }
22 void dfs(int v,int fa){
23     int d=g[v].size();
24     if(fa==-1)
25         wide[v]=0;
26     else
27         wide[v]=wide[fa]+1;
28     if(wide[v]>wide_max)
29         wide_max=wide[v];
30     for(int i=0;i<d;i++){
31         int k=g[v][i];
32         if(k!=fa)
33             dfs(k,f[k]=v);
34     }
35 }
36 int treedp(int root){
37     f[root]=-1;
38     wide_max=-1;
39     dfs(root,-1);
40     for(int i=wide_max;i>=0;i--){
41         for(int j=1;j<=n;j++){
42             if(wide[j]==i){
43                 dp[j]=max(son[j],gson[j]+1);
44                 if(i>=1)
45                     son[f[j]]+=dp[j];
46                 if(i>=2)
47                     gson[f[f[j]]]+=dp[j];
48             }
49         }
50     }
51     return dp[root];
52 }
53 int solve(){
54     int ans=0;
55     for(int i=1;i<=n;i++){
56         memset(son,0,sizeof(son));
57         memset(gson,0,sizeof(gson));
58         ans=max(ans,treedp(i));
59     }
60     return ans;
61 }
62 int main()
63 {
64     init();
65     int ans=solve();
66     printf("%d\n",ans);
67     return 0;
68 }