cf1179D

cf1179D

链接

cf

思路

csdn
很玄学，正解是斜率优化dp,但被一个奇妙的贪心过了。

代码

#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int _=5e5+7;
int n,siz[_],S,id;
ll f[_],ans;
vector<int> G[_];
void dfs1(int u,int fa) {
	siz[u]=1;
	for(auto v:G[u]) {
		if(v==fa) continue;
		dfs1(v,u),siz[u]+=siz[v];
	}
}
void dfs2(int u,int fa) {
	for(auto v:G[u]) {
		if(v==fa) continue;
		f[v]=f[u]+1LL*(siz[u]-siz[v])*siz[v];
		dfs2(v,u);
	}
	if(f[u]>f[id]) id=u;
}
int main() {
	scanf("%d",&n);
	for(int i=1,u,v;i<n;++i) {
		scanf("%d%d",&u,&v);
		G[u].push_back(v),G[v].push_back(u);
	}
	S=1;
	f[1]=0,dfs1(S,0),dfs2(S,0);
	memset(siz,0,sizeof(siz));
	memset(f,0,sizeof(f));
	S=id;
	f[1]=0,dfs1(S,0),dfs2(S,0);
	ans=1LL*n*(n-1)/2+f[id];
	cout<<ans<<"\n";
	return 0;
}