题解

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<vector>
#include<queue>

using namespace std;

#define il inline
typedef long long ll;

ll gcd(ll a,ll b){
	return b==0?a:gcd(b,a%b);
}

typedef double Grad;

int n;
struct Node{
	int x,y;
	int p;
	char c;
}a[1005];
bool cmp(Node a,Node b){
	return a.x!=b.x?a.x<b.x:a.y>b.y;
}

int s[1005];

struct Line{
	int i1,i2;	// id
	Grad G;
	Line(){} Line(int a_,int b_){i1=a_,i2=b_;G=1.0*(a[i2].y-a[i1].y)/(a[i2].x-a[i1].x);}
	bool operator<(Line b){
		return G<b.G;
	}
}ls[1000006];
int ms=0;

vector<pair<int,int> > sw[1000006];int st;

int did[1006],id[1006];

int main(){

	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		scanf("%d%d",&a[i].x,&a[i].y);
		a[i].c=getchar(); while(a[i].c!='R' && a[i].c!='B'){ a[i].c=getchar(); }
	}
	sort(a+1,a+n+1,cmp);
	
	for(int i=1;i<=n;i++){
		s[i]=((a[i].c=='R')?0:1);
	}

	for(int i=1;i<=n;i++){
		for(int j=i+1;j<=n;j++){
			ls[++ms]=Line(i,j);
		}
	}
	sort(ls+1,ls+ms+1);
	st=1;sw[1].push_back(make_pair(ls[1].i1,ls[1].i2));
	for(int i=2;i<=ms;i++){
		if(ls[i].G!=ls[i-1].G){
			st++;
		}
		sw[st].push_back(make_pair(ls[i].i1,ls[i].i2));
	}
   
	int ans=0;
	int l=1;		// 永远焕发光芒的暴力维护区间
	for(int j=1;j<=n;j++){
		if(s[j]==1){
			l=j+1;
		}
		if(s[l]==0 && s[j]==0){ans=max(ans,j-l+1);}
	}

	for(int i=1;i<=n;i++){id[i]=did[i]=i;}

	for(int i=1;i<=st;i++){
		for(int j=0;j<sw[i].size();j++){
			int x=sw[i][j].first,y=sw[i][j].second,u,v;

			swap(did[x],did[y]);
			swap(id[did[x]],id[did[y]]);
			u=s[did[x]],v=s[did[y]];
			s[did[x]]=v,s[did[y]]=u;	// 完全没用的调试信息
		}
		
		int l=1;	// 运用反复的修辞手法
		for(int j=1;j<=n;j++){
			if(s[j]==1){
				l=j+1;
			}
			if(s[l]==0 && s[j]==0){ans=max(ans,j-l+1);}
		}
		
	}

	printf("%d\n",ans);

	return 0;
}