CF 1029E Tree with Small Distances

Posted 2021-01-16 lnxcj

小胖守皇宫！

又双叒叕水了一篇

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5 int n,m,cnt,ans;
 6 int fa[200005];
 7 int dep[200005];
 8 int dp[200005][3];
 9 int head[200005];
10 struct Edge{
11     int fr;
12     int to;
13     int nxt;
14 }edge[400005];
15 void init(){
16     memset(head,-1,sizeof(head));
17 }
18 void addedge(int f,int t){
19     cnt++;
20     edge[cnt].fr=f;
21     edge[cnt].to=t;
22     edge[cnt].nxt=head[f];
23     head[f]=cnt;
24 }
25 void dfs(int u){
26     int tmp=0x3f3f3f3f;
27     for(int i=head[u];i!=-1;i=edge[i].nxt){
28         int v=edge[i].to;
29         if(v==fa[u])continue;
30         fa[v]=u;dep[v]=dep[u]+1;
31         dfs(v);
32         dp[u][1]+=min(dp[v][0],min(dp[v][2],dp[v][1]));
33         dp[u][2]+=min(dp[v][2],dp[v][1]);
34         tmp=min(dp[v][1]-dp[v][2],tmp);
35         dp[u][0]+=min(dp[v][1],dp[v][2]);
36     }
37     if(tmp>0)dp[u][2]+=tmp;
38     if(dep[u]>1)dp[u][1]+=1;
39 }
40 int main(){
41     init();
42     scanf("%d",&n);
43     for(int i=1;i<n;i++){
44         int u,v;
45         scanf("%d%d",&u,&v);
46         addedge(u,v);
47         addedge(v,u);
48     }
49     dfs(1);
50     printf("%d
",dp[1][1]);
51     return 0;
52 }