题解:【ICPC WF 2021 K】 Take On Meme

发布时间 2023-07-25 11:55:22作者: LgxTpre

题目链接

可以直接求闵可夫斯基和,这里介绍一种官解。

按照题面的两个评分尺度构建坐标系,将所有可能的 \(1\) 号节点分值放在平面上,那么最后的答案一定在凸包上。如果我们知道答案的最终方向,那么问题就比较简单了:就是直接寻找特定方向上最远的点(那么就是找一个点使其与选定点的点积最大),只需要让和这个方向点积的贡献最短就行了。虽然我们并不知道方向是什么,不过可以随便钦定一个方向,求点积最大和最小的点,这样一定可以找到凸包上的两个点,这个可以直接树形 DP 做。再以这两个点的连线的垂线为方向,如果凸包上还有点那么一定可以找到新的凸包上的点。反复重复这个过程,知道找出的点积最大和最小的点重合,这时候找齐了凸包上的所有点。找点的时候顺便直接统计答案即可。

这样复杂度是凸包上的点数乘 \(n\) 的,因为做一遍树形 DP 是 \(\mathcal O(n)\),一次只能找到凸包上两个点。不过这样就留下了一个问题:凸包上到底有多少个点,复杂度是否正确?注意到给定的点的坐标都是整数,整点凸包上的点的数量级是我们已经解决的问题。于是总复杂度为 \(\mathcal O(T^{\frac{2}{3}} n)\),其中 \(T \leq 10^7\)

#include<bits/stdc++.h>
#define int long long
#define ld long double
#define ui unsigned int
#define ull unsigned long long
#define eb emplace_back
#define pb pop_back
#define ins insert
#define mp make_pair
#define pii pair<int,int>
#define fi first
#define se second
#define power(x) ((x)*(x))
#define gcd(x,y) (__gcd((x),(y)))
#define lcm(x,y) ((x)*(y)/gcd((x),(y)))
#define lg(x,y)  (__lg((x),(y)))
using namespace std;

namespace FastIO
{
    template<typename T=int> inline T read()
    {
        T s=0,w=1; char c=getchar();
        while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
        while(isdigit(c)) s=(s*10)+(c^48),c=getchar();
        return s*w;
    }
    template<typename T> inline void read(T &s)
    {
        s=0; int w=1; char c=getchar();
        while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
        while(isdigit(c)) s=(s*10)+(c^48),c=getchar();
        s=s*w;
    }
    template<typename T,typename... Args> inline void read(T &x,Args &...args)
    {
        read(x),read(args...);
    }
    template<typename T> inline void write(T x,char ch)
    {
        if(x<0) x=-x,putchar('-');
        static char stk[25]; int top=0;
        do {stk[top++]=x%10+'0',x/=10;} while(x);
        while(top) putchar(stk[--top]);
        putchar(ch);
        return;
    }
}
using namespace FastIO;

namespace MTool
{   
    #define TA template<typename T,typename... Args>
    #define TT template<typename T>
    static const int Mod=998244353;
    TT inline void Swp(T &a,T &b) {T t=a;a=b;b=t;}
    TT inline void cmax(T &a,T b) {a=a>b?a:b;}
    TT inline void cmin(T &a,T b) {a=a<b?a:b;}
    TT inline void Madd(T &a,T b) {a=a+b>Mod?a+b-Mod:a+b;}
    TT inline void Mdel(T &a,T b) {a=a-b<0?a-b+Mod:a-b;}
    TT inline void Mmul(T &a,T b) {a=a*b%Mod;}
    TT inline void Mmod(T &a) {a=(a%Mod+Mod)%Mod;}
    TT inline T Cadd(T a,T b) {return a+b>=Mod?a+b-Mod:a+b;}
    TT inline T Cdel(T a,T b) {return a-b<0?a-b+Mod:a-b;}
    TT inline T Cmul(T a,T b) {return a*b%Mod;}
    TT inline T Cmod(T a) {return (a%Mod+Mod)%Mod;}
    TA inline void Madd(T &a,T b,Args... args) {Madd(a,Cadd(b,args...));}
    TA inline void Mdel(T &a,T b,Args... args) {Mdel(a,Cadd(b,args...));}
    TA inline void Mmul(T &a,T b,Args... args) {Mmul(a,Cmul(b,args...));}
    TA inline T Cadd(T a,T b,Args... args) {return Cadd(Cadd(a,b),args...);}
    TA inline T Cdel(T a,T b,Args... args) {return Cdel(Cdel(a,b),args...);}
    TA inline T Cmul(T a,T b,Args... args) {return Cmul(Cmul(a,b),args...);}
    TT inline T qpow(T a,T b) {int res=1; while(b) {if(b&1) Mmul(res,a); Mmul(a,a); b>>=1;} return res;}
    TT inline T qmul(T a,T b) {int res=0; while(b) {if(b&1) Madd(res,a); Madd(a,a); b>>=1;} return res;}
    TT inline T spow(T a,T b) {int res=1; while(b) {if(b&1) res=qmul(res,a); a=qmul(a,a); b>>=1;} return res;}
    TT inline void exgcd(T A,T B,T &X,T &Y) {if(!B) return X=1,Y=0,void(); exgcd(B,A%B,Y,X),Y-=X*(A/B);}
    TT inline T Ginv(T x) {T A=0,B=0; exgcd(x,Mod,A,B); return Cmod(A);}
    #undef TT
    #undef TA
}
using namespace MTool;

inline void file()
{
    freopen(".in","r",stdin);
    freopen(".out","w",stdout);
    return;
}

bool Mbe;

namespace LgxTpre
{
    static const int MAX=10010;
    static const int inf=2147483647;
    static const int INF=4557430888798830399;
    static const int mod=1e9+7;
    static const int bas=131;
	
	namespace Geometry
	{
		struct Point
		{
			int x,y;
			Point(int X=0,int Y=0):x(X),y(Y) {}
			inline friend Point operator + (Point a,Point b) {return Point(a.x+b.x,a.y+b.y);}
			inline friend Point operator - (Point a,Point b) {return Point(a.x-b.x,a.y-b.y);}
			template<typename T> inline friend Point operator * (Point a,T b) {return Point(a.x*b,a.y*b);}
			template<typename T> inline friend Point operator / (Point a,T b) {return Point(a.x/b,a.y/b);}
			inline friend Point operator * (Point a,Point b) {return Point(a.x*b.x-a.y*b.y,a.y*b.x+a.x*b.y);}
			inline Point operator += (Point &T) {*this=*this+T; return *this;}
			inline Point operator -= (Point &T) {*this=*this-T; return *this;}
			template<typename T> inline Point operator *= (T &x) {*this=*this*x; return *this;}
			template<typename T> inline Point operator /= (T &x) {*this=*this/x; return *this;}
			inline Point operator *= (Point &T) {*this=*this*T; return *this;}
			inline friend bool operator == (Point a,Point b) {return a.x==b.x&&a.y==b.y;}
		};
		inline int Dot(Point a,Point b) {return a.x*b.x+a.y*b.y;}
		inline int Cross(Point a,Point b) {return a.x*b.y-a.y*b.x;}
		inline int Norm(Point a) {return sqrt(Dot(a,a));}
	}
	using namespace Geometry;
	
	int n,k,ans;
	Point p[MAX];
	vector<int> G[MAX];
	
    inline void lmy_forever()
    {
    	auto Hull=[&](Point P)->pair<Point,Point>
    	{
    		auto comp=[&](Point A,Point B)->bool
    		{
    			return Dot(P,A)<Dot(P,B);
			};
    		auto dfs=[&](auto dfs,int now)->pair<Point,Point>
    		{
    			if(G[now].empty()) return mp(p[now],p[now]);
    			auto [sl,sr]=dfs(dfs,G[now][0]);
    			Point vl,vr; vl=vr=sl+sr;
    			for(int i=1;i<((int)G[now].size());++i)
    			{
    				auto [l,r]=dfs(dfs,G[now][i]);
    				sl+=l,sr+=r;
    				if(comp(l+r,vl)) vl=l+r;
    				if(comp(vr,l+r)) vr=l+r;
				}
				return mp(vl-sr,vr-sl);
			};
			auto [l,r]=dfs(dfs,1);
			cmax(ans,Dot(l,l)),cmax(ans,Dot(r,r));
			return mp(l,r);
		};
		
		auto solve=[&](auto solve,Point a,Point b)->void
		{
			if(a==b) return;
			int x=(b-a).x,y=(b-a).y;
			Point c={-y,x};
			auto [_,d]=Hull(c);
			if(Dot(d,c)>max(Dot(a,c),Dot(b,c))) solve(solve,a,d),solve(solve,d,b);
		};
    	
    	read(n);
    	for(int i=1;i<=n;++i)
    	{
    		read(k);
    		if(!k) read(p[i].x,p[i].y);
    		else for(int j=1;j<=k;++j) G[i].eb(read());
		}
		auto [a,b]=Hull((Point){1,0});
		solve(solve,a,b);
		write(ans,'\n');
        return;
    }
}

bool Med;

int T;

signed main()
{
//  file();
    fprintf(stderr,"%.3lf MB\n",abs(&Med-&Mbe)/1048576.0);
    int Tbe=clock();
    LgxTpre::lmy_forever();
    int Ted=clock();
    cerr<<1e3*(Ted-Tbe)/CLOCKS_PER_SEC<<" ms\n";
    return (0-0);
}