解题：POI 2013 Triumphal arch

Posted 2021-01-07 ydnhaha

题面

 

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5 const int N=300005;
 6 int n,t1,t2,cnt,l,r,mid,ans;
 7 int p[N],noww[2*N],goal[2*N];
 8 int son[N],dp[N];
 9 void link(int f,int t)
10 {
11     noww[++cnt]=p[f];
12     goal[cnt]=t,p[f]=cnt;
13 }
14 void MARK(int nde,int fth)
15 {
16     for(int i=p[nde];i;i=noww[i])
17         if(goal[i]!=fth) MARK(goal[i],nde),son[nde]++;
18 }
19 void DFS(int nde,int fth)
20 {
21     int tmp=0;
22     for(int i=p[nde];i;i=noww[i])
23         if(goal[i]!=fth) DFS(goal[i],nde),tmp+=dp[goal[i]];
24     dp[nde]=max(tmp+son[nde]-mid,0);
25 }
26 bool check(int x)
27 {
28     memset(dp,0xcf,sizeof dp);
29     DFS(1,0); return !dp[1];
30 }
31 int main ()
32 {
33     scanf("%d",&n),r=n;
34     for(int i=1;i<n;i++)
35     {
36         scanf("%d%d",&t1,&t2);
37         link(t1,t2),link(t2,t1);
38     }
39     MARK(1,0);
40     while(l<=r)
41     {
42         mid=(l+r)/2;
43         if(check(mid)) r=mid-1,ans=mid;
44         else l=mid+1;
45     }
46     printf("%d",ans);
47     return 0;
48 }

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