Submission #537875

#	Time	Username	Problem	Language	Result	Execution time	Memory
537875		michao	Monochrome Points (JOI20_monochrome)	C++14	100 / 100	109 ms	5708 KiB

monochrome

#include <bits/stdc++.h>
#define int long long
#define mp make_pair
#define pb push_back
#define ld long double
#define pii pair<int,int>
#define sz(x) (int)x.size()
#define piii pair<pii,pii>
#define precise cout<<fixed<<setprecision(10)
#define st first
#define nd second
#define ins insert
#define vi vector<int>
#define BOOST ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
using namespace std;
const int MAX=2e5+5;
const int STALA=30;
vi b,w;
char s[MAX*2];
int ans=0;
int n;

int ile(int x,int y){
	if (x>y)swap(x,y);
	int between=y-x-1;
	return min(n*2-2-between,between);
}

int f(int shift){
	int sum=0;
	assert(sz(b)==sz(w) && sz(b)==n);
	for (int i=0;i<n;i++){
		int x=b[i];
		int y=w[(i+shift)%n];
		//if (shift==1)cout<<"TERAZ "<<x<<" "<<y<<" "<<ile(x,y)<<"\n";
		sum+=ile(x,y);
	}
	return sum/2;
}

int ternary(int l,int r){
	int ip=l,ik=r;
	for (int i=0;i<STALA;i++){
		if (abs(ik-ip)<5)break;
		int dodaj=(ik-ip)/3;
		int mid1=ip+dodaj;
		int mid2=ik-dodaj;
		if (f(mid1)<f(mid2))ip=mid1;
		else ik=mid2;
	}
	int maxi=0;
	for (int i=ip-7;i<=ik+7;i++){
		if (i>=0 && i<=n-1)maxi=max(maxi,f(i));
	}
	return maxi;
}
int32_t main(){
  BOOST;
  cin>>n;
  for (int i=0;i<n*2;i++){
		cin>>s[i];
		if (s[i]=='B')b.pb(i);
		else w.pb(i);
  }
  
  if (f(0)>=f(n-1)){
		int ip=0,ik=n;
		while (ip+1<ik){
			int mid=(ip+ik)>>1;
			if (f(mid)>=f(0))ip=mid;
			else ik=mid;
		}
		cout<<ternary(0,ip);
  }
  else{
		int ip=-1,ik=n-1;
		while (ip+1<ik){
			int mid=(ip+ik)>>1;
			if (f(mid)>=f(n-1))ik=mid;
			else ip=mid;
		}
		cout<<ternary(ik,n-1);
  }
  
  return 0; 
}

• Subtask 1: 4 / 4
• Subtask 2: 21 / 21
• Subtask 3: 10 / 10
• Subtask 4: 65 / 65