Submission #63593

#	Time	Username	Problem	Language	Result	Execution time	Memory
63593		zetapi	Alternating Current (BOI18_alternating)	C++14	100 / 100	107 ms	15480 KiB

alternating

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

#define pb  push_back
#define mp  make_pair
#define int long long
#define itr ::iterator 

#define start  first
#define length second.first

typedef pair<int,int>  pii;

const int MAX=1e5;

bool cmp(const pair<int,pii> X,const pair<int,pii> Y)
{
	if(X.start==Y.start)
		return X.length>Y.length;
	return X.start<Y.start;
}

vector<pair<int,pii>> arr;
vector<int> vec,Enclosed[MAX];

int N,M,X,Y,par[MAX],mark[MAX];	
int len,cur,pre;

int root(int X)
{
	if(par[X]==X)
		return X;
	return par[X]=root(par[X]);
}

bool Subset(int X,int Y)
{
	int RelativeStart=(arr[X].start-arr[Y].start+N)%N;
	return RelativeStart+arr[X].length<=arr[Y].length;
}

void Alternate()
{
	for(int A=0;A<vec.size();A++)
		mark[arr[vec[A]].second.second]=A%2;
	for(int A=0;A<vec.size();A++)
	{
		for(auto B:Enclosed[vec[A]])
			mark[arr[B].second.second]=mark[arr[vec[A]].second.second]^1;
	}
	return ;
}

bool ok()
{
	int BIT[MAX];
	for(int A=0;A<2;A++)
	{
		for(int B=0;B<N;B++)
			BIT[B]=0;
		for(int B=0;B<M;B++)
		{
			if(mark[arr[B].second.second]!=A)
				continue;
			//cout<<"original index "<<B<<" start "<<arr[B].start<<"  length "<<arr[B].length<<"\n";
			if(arr[B].start+arr[B].length-1>=N)
			{
				BIT[0]++;
				BIT[arr[B].start]++;
				BIT[(arr[B].start+arr[B].length-1)%N+1]--;
			}
			else
			{
				BIT[arr[B].start]++;
				BIT[arr[B].start+arr[B].length]--;
			}	
		}
		for(int A=0;A<N;A++)
		{
			BIT[A+1]+=BIT[A];
			if(!BIT[A])
				return false;
		}
	}
	return true;
}

bool ok(int L,int R,int col)
{
	int Start=vec[L];
	int End=vec[R];
	int len=(End-Start+M-1)%M+1;
	int high=arr[Start].start;
	for(int A=0;A<len;A++)
	{
		int cur=(Start+A)%M;
		if(mark[arr[cur].second.second]!=col)
			continue;
		int now=arr[cur].start;
		if(cur<Start)
			now+=N;
		if(now>high)
			return false;
		high=max(high,now+arr[cur].length);
	}
	int now=arr[End].start;
	if(End<=Start)
		now+=N;
	return now<=high;
}

void color(int X,int C)
{
	if(C>=0)
		mark[arr[vec[X]].second.second]=C;
	for(auto A:Enclosed[vec[X]])
		mark[arr[A].second.second]=!mark[arr[vec[X]].second.second];
	return ;
}

signed main()
{
	ios_base::sync_with_stdio(false);

	cin>>N>>M;
	for(int A=0;A<M;A++)
	{
		par[A]=A;
		cin>>X>>Y;
		X--;
		Y--;
		len=(Y-X+N)%N+1;
		arr.pb(mp(X,mp(len,A)));
	}	
	sort(arr.begin(),arr.end(),cmp);
	pre=0;
	for(int A=1;A<2*M;A++)
	{
		cur=A%M;
		if(Subset(cur,pre))
			par[cur]=pre;
		else
			pre=cur;	
	}
	for(int A=0;A<M;A++)
	{
		cur=root(A);
		if(A==cur)
			vec.pb(A);
		else
			Enclosed[cur].pb(A);
	}
	if(!(vec.size()%2))
	{
		Alternate();
		if(ok())
			for(int A=0;A<M;A++)
				cout<<mark[A];
		else
			cout<<"impossible\n";
		return 0;
	}
	else
	{
		for(int A=0;A<vec.size();A++)
		{
			int a=(A+0+vec.size())%vec.size();
			int b=(A+1+vec.size())%vec.size();
			int c=(A+2+vec.size())%vec.size();
			int d=(A+3+vec.size())%vec.size();	
			color(a,1);
			color(b,0);
			color(c,0);
			color(d,1);
			if(ok(a,d,1))
			{
				for(int A=0;A<vec.size();A++)
				{
					int cur=(d+A)%vec.size();
					if(cur==a or cur==b or cur==c or cur==d)
						continue;
					mark[arr[vec[cur]].second.second]=!mark[arr[vec[(cur-1+vec.size())%vec.size()]].second.second];
				}
				for(int A=0;A<vec.size();A++)
					color(A,-1);
				if(ok())
				{
					for(int A=0;A<M;A++)
						cout<<mark[A];
					return 0;
				}
				else
					cout<<"impossible";
				return 0;
			}
		}
	}
	cout<<"impossible";
	return 0;
}

Compilation message (stderr)

alternating.cpp: In function 'void Alternate()':
alternating.cpp:44:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int A=0;A<vec.size();A++)
              ~^~~~~~~~~~~
alternating.cpp:46:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int A=0;A<vec.size();A++)
              ~^~~~~~~~~~~
alternating.cpp: In function 'int main()':
alternating.cpp:165:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int A=0;A<vec.size();A++)
               ~^~~~~~~~~~~
alternating.cpp:177:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int A=0;A<vec.size();A++)
                 ~^~~~~~~~~~~
alternating.cpp:184:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int A=0;A<vec.size();A++)
                 ~^~~~~~~~~~~

• Subtask 1: 13 / 13
• Subtask 2: 20 / 20
• Subtask 3: 22 / 22
• Subtask 4: 19 / 19
• Subtask 5: 26 / 26