Vijos P1476 旅游规划(csapc) 聪哥说我根本不理解树形DP23333333333

 1 #include<queue>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 bool p[200003];
 7 int point[200003],next[400003],v[400003],cnt=0,N,kk,dist[200003],first[200003],second[200003];
 8 void insect(int u,int vv){next[cnt]=point[u];point[u]=cnt;v[cnt]=vv;cnt++;}
 9 void bfs(int k)
10 {
11     queue<int>q; memset(dist,0,sizeof(dist));
12     q.push(k); dist[k]=1; int now,i;
13     while (!q.empty())
14     {
15         now=q.front(); q.pop();
16         for (i=point[now];i!=-1;i=next[i])
17          if (dist[v[i]]==0){dist[v[i]]=dist[now]+1;q.push(v[i]);if (dist[v[i]]>dist[kk]) kk=v[i];}
18     }
19 }
20 void dp(int x)
21 {
22     int i=0; p[x]=1;
23     for (i=point[x];i!=-1;i=next[i])
24     {
25         if (p[v[i]]==0)
26         {
27             dp(v[i]);
28             if (first[x]<=first[v[i]]+1) {second[x]=first[x];first[x]=first[v[i]]+1;}
29             else if (second[x]<=first[v[i]]+1) second[x]=first[v[i]]+1;
30         }
31     }if (first[x]==0) first[x]=1;
32 }
33 void work2(int x)
34 {
35     int i; p[x]=1;
36     for (i=point[x];i!=-1;i=next[i])
37      if ((p[v[i]]==0)&&(first[v[i]]==first[x]-1))
38       work2(v[i]);
39 }
40 void work(int x,int fir,int sec)
41 {
42     int i; p[x]=1;
43     for (i=point[x];i!=-1;i=next[i])
44      if (((first[v[i]]==fir-1)||(first[v[i]]==sec-1))) work2(v[i]);
45 }
46 int main()
47 {
48     memset(next,-1,sizeof(next));
49     memset(v,0,sizeof(v));
50     memset(point,-1,sizeof(point));
51     scanf("%d\n",&N);
52     int i,x,y,begin,table;
53     for (i=1;i<N;++i){scanf("%d %d\n",&x,&y);insect(x,y);insect(y,x);}
54     bfs(0); begin=kk; bfs(begin); table=dist[kk]; memset(p,0,sizeof(p));
55     dp(0); memset(p,0,sizeof(p));
56     for (i=0;i<=N;++i) if (first[i]+second[i]==table+1) work(i,first[i],second[i]);
57     for (i=0;i<=N;++i) if (p[i]) printf("%d\n",i);
58     return 0;
59 }