Submission #724943

#	Time	Username	Problem	Language	Result	Execution time	Memory
724943		Rafi22	Alternating Current (BOI18_alternating)	C++14	100 / 100	55 ms	10476 KiB

alternating

#include <bits/stdc++.h>

using namespace std;

#define endl '\n'
#define st first
#define nd second
#define pb push_back
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define ll long long
ll mod=1000000007;
int inf=1000000007;
ll infl=1000000000000000007;

void gg()
{
    cout<<"impossible";
    exit(0);
}

const int N=100007,pot=1<<17;

bool ans[N];
int l[N];
int r[N];
int ile[N];
int L[N];

vector<int>V[N];
int o[N];

pair<int,int> seg[2*pot+7];

pair<int,int> que(int v)
{
    v+=pot-1;
    pair<int,int>p={inf,0};
    while(v>0)
    {
        p=min(p,seg[v]);
        v/=2;
    }
    return p;
}
void ins(int v,int a,int b,int l,int r,int x,int i)
{
    if(a<=l&&b>=r)
    {
        seg[v]=min(seg[v], {x,i});
        return ;
    }
    if(r<a||l>b) return ;
    ins(2*v,a,b,l,(l+r)/2,x,i);
    ins(2*v+1,a,b,(l+r)/2+1,r,x,i);
}


int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n,m;
    cin>>n>>m;
    int mx=0,k;
    for(int i=1;i<=m;i++)
    {
        cin>>l[i]>>r[i];
        l[i]--;
        r[i]--;
        if((r[i]-l[i]+n)%n+1>mx)
        {
            mx=(r[i]-l[i]+n)%n+1;
            k=i;
        }
    }
    ans[k]=1;
    int t=l[k];
    for(int i=1;i<=m;i++)
    {
        l[i]=(l[i]-t+n)%n;
        r[i]=(r[i]-t+n)%n;
     //   cout<<l[i]<<" "<<r[i]<<endl;
        if(l[i]<=r[i])
        {
            ile[l[i]]++;
            ile[r[i]+1]--;
        }
        else
        {
            ile[l[i]]++;
            ile[0]++;
            ile[r[i]+1]--;
        }
    }
    int act=0;
    L[0]=-1;
    for(int i=0;i<n;i++)
    {
        act+=ile[i];
        if(act<2) gg();
        if(i>0) L[i]=L[i-1];
        if(act==2) L[i]=i;
    }
    for(int i=1;i<=m;i++) if(i!=k) V[l[i]].pb(i);
    for(int i=1;i<2*pot;i++) seg[i].st=inf;
    ins(1,L[r[k]]+2,r[k]+2,1,pot,r[k]+1,k);
    int X=-1;
    if(r[k]==n-1) X=k;
    for(int j=0;j<n;j++)
    {
        for(auto i:V[j])
        {
            pair<int,int>p=que(l[i]+1);
            o[i]=p.nd;
            if(o[i]!=0&&r[i]==n-1) X=i;
            if(l[i]<=r[i]) ins(1,max(p.st,L[r[i]]+1)+1,r[i]+2,1,pot,r[i]+1,i);
            else
            {
                if(o[i]!=0&&L[r[i]]==-1) X=i;
            }
        }
    }
    if(X==-1) gg();
    while(X>0)
    {
        ans[X]=1;
        X=o[X];
    }
    for(int i=1;i<=m;i++) cout<<ans[i];

    return 0;
}

Compilation message (stderr)

alternating.cpp: In function 'int main()':
alternating.cpp:78:11: warning: 'k' may be used uninitialized in this function [-Wmaybe-uninitialized]
   78 |     ans[k]=1;
      |     ~~~~~~^~

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