Submission #379305

#	Time	Username	Problem	Language	Result	Execution time	Memory
379305		eulerdesoja	Building 4 (JOI20_building4)	C++14	100 / 100	362 ms	103788 KiB

building4

#include<bits/stdc++.h>
#include<fstream>
using namespace std;

#define ll long long
#define pb push_back
#define sz(x) int(x.size())

typedef pair<int,int>ii;
typedef vector<int> vi;

//we try to guess how many A's we will use on the building
//aparently (need to prove) the possibilities are contiguous
//i just need to find the minimum and maximum possible and check if n it is in it

const int mxn=1e6+5;
int n,a[2][mxn];
int dpmin[mxn][2],dpmax[mxn][2];
int smin(int i,int last){
	if(i==0)return 0;
	if(dpmin[i][last]!=-1)return dpmin[i][last];

	int ans=1e9+5;

	for(int j=0;j<2;j++){
		if(a[j][i]<=a[last][i+1])ans=min(ans,smin(i-1,j)+j);
	}

	return dpmin[i][last]=ans;
}

int smax(int i,int last){
	if(i==0)return 0;
	if(dpmax[i][last]!=-1)return dpmax[i][last];

	int ans=0;
	for(int j=0;j<2;j++){
		if(a[j][i]<=a[last][i+1])ans=max(ans,smax(i-1,j)+j);
	}
	return dpmax[i][last]=ans;
}
int32_t main(){
	ios_base::sync_with_stdio(0);cin.tie(0);
	cin>>n;n*=2;

	for(int i=1;i<=n;i++)cin>>a[0][i];
	for(int i=1;i<=n;i++)cin>>a[1][i];
	a[0][n+1]=a[1][n+1]=1e9+5;
	
	memset(dpmin,-1,sizeof(dpmin));
	memset(dpmax,-1,sizeof(dpmax));

	int x=n/2,y=n/2,last=0;

	string s;
	for(int i=n;i>=1;i--){
		if(smin(i,last)<=y && y<=smax(i,last)){
			int mn=smin(i-1,0),mx=smax(i-1,0);
			if(mn<=y && y<=mx && x && a[0][i]<=a[last][i+1]){
				x--;
				s+='A';
				last=0;
			}
			else{
				y--;
				s+='B';
				last=1;
			}
		}
		else{
			cout<<-1<<"\n";
			return 0;
		}
	}
	reverse(s.begin(),s.end());
	if(x || y)cout<<-1<<"\n";
	else cout<<s<<"\n";

	return 0;
}

• Subtask 1: 11 / 11
• Subtask 2: 89 / 89