Submission #1259896

#	Time	Username	Problem	Language	Result	Execution time	Memory
1259896		Zbyszek99	Alternating Current (BOI18_alternating)	C++20	19 / 100	45 ms	6612 KiB

alternating

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define ld long double
#define ull unsigned long long
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<long long, long long>
#define vi vector<int>
#define vl vector<long long>
#define pb push_back
#define rep(i, b) for(int i = 0; i < (b); ++i)
#define rep2(i,a,b) for(int i = a; i <= (b); ++i)
#define rep3(i,a,b,c) for(int i = a; i <= (b); i+=c)
#define count_bits(x) __builtin_popcountll((x))
#define all(x) (x).begin(),(x).end()
#define siz(x) (int)(x).size()
#define forall(it,x) for(auto& it:(x))
using namespace __gnu_pbds;
using namespace std;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
//mt19937 mt;void random_start(){mt.seed(chrono::time_point_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()).time_since_epoch().count());}
//ll los(ll a, ll b) {return a + (mt() % (b-a+1));}
const int INF = 1e9+50;
const ll INF_L = 1e18+40;
const ll MOD = 1e9+7;

int n,m;
int rel_ind[100001];
bool ans[100001];
int parent[100001];
int sum[100001];
int tri_sum[100001];
vector<pii> segs;
vi big;
vi rest;

bool comp(pair<int,pii> a, pair<int,pii> b)
{
    return (a.ss.ss-a.ss.ff+m)%m > (b.ss.ss-b.ss.ff+m)%m;
}

int main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    //random_start();
    cin >> m >> n;
    vector<pair<int,pii>> segs2;
    rep(i,n)
    {
        int a,b;
        cin >> a >> b;
        a--;
        b--;
        segs2.pb({i,{a,b}});
    }
    sort(all(segs2),comp);
    rep(i,siz(segs2))
    {
        rel_ind[i] = segs2[i].ff;
        segs.pb(segs2[i].ss);
    }
    set<pii> big_segs;
    int ind = 0;
    vi rest;
    forall(it,segs)
    {
        int prv = -1;
        auto ptr= big_segs.lower_bound({it.ff,1e9});
        if(ptr != big_segs.begin())
        {
            prv = (*(--ptr)).ss;
        }
        else
        {
            if(siz(big_segs) != 0) prv = (*(--big_segs.end())).ss;
        }
        parent[ind] = prv;
        if(prv == -1) big_segs.insert({it.ff,ind});
        else
        {
            if(it.ff <= it.ss)
            {
                if(segs[prv].ff <= segs[prv].ss)
                {
                    if(!(segs[prv].ff <= it.ff && segs[prv].ss >= it.ss)) big_segs.insert({it.ff,ind});
                    else rest.pb(ind);
                }
                else
                {
                    if(!(segs[prv].ff <= it.ff || segs[prv].ss >= it.ss)) big_segs.insert({it.ff,ind});
                    else rest.pb(ind);
                }
            }
            else
            {
                if(segs[prv].ff <= segs[prv].ss)
                {
                    big_segs.insert({it.ff,ind});
                }
                else
                {
                    if(!(segs[prv].ff <= it.ff && segs[prv].ss >= it.ss) && segs[prv].ff != (segs[prv].ss+1)%m) big_segs.insert({it.ff,ind});
                    else rest.pb(ind);
                }
            }
        }
        ind++;
    }   
    rep(i,n)
    {
        if(segs[i].ff <= segs[i].ss)
        {
            sum[segs[i].ff]++;
            sum[segs[i].ss+1]--;
        }
        else
        {
            sum[0]++;
            sum[segs[i].ss+1]--;
            sum[segs[i].ff]++;
        }
    } 
    vi big;
    forall(it,big_segs) big.pb(it.ss);
    int cur_sum = 0;
    rep(i,m)
    {
        cur_sum += sum[i];
        sum[i] = cur_sum;
        if(sum[i] <= 1)
        {
            cout << "impossible\n";
            return 0;
        }
    }
    cur_sum = 0;
    rep(i,m)
    {
        if(sum[i] > 2) cur_sum++;
        tri_sum[i+1] = cur_sum;
    }
    if(siz(big)%2==0)
    {
        int color = 0;
        forall(it,big)
        {
            ans[rel_ind[it]] = color;
            color ^= 1;
        }
        forall(it,rest)
        {
            ans[rel_ind[it]] = ans[rel_ind[parent[it]]]^1;
        }
        rep(i,n) cout << ans[i];
        return 0;
    }
    if(siz(big) == 1)
    {
        ans[rel_ind[big[0]]] = 1;
        rep(i,n) cout << ans[i];
        return 0;
    }
    int pot = -1;
    rep(i,siz(big))
    {
        int l = segs[big[(i+1)%siz(big)]].ff;
        int r = segs[big[i]].ss;
        bool is = 0;
        if(l <= r)
        {
            is = (tri_sum[r+1]-tri_sum[l] == r-l+1);
        }
        else
        {
            is = (tri_sum[m]-tri_sum[l]+tri_sum[r+1] == (r-l+1+m)%m);
        }
        if(is) pot = i;
    }
    if(pot == -1) cout << "impossible\n";
    else
    {
        int color = 0;
        rep(i,siz(big))
        {
            if((i-1+siz(big))%siz(big) == pot)
            {
                ans[rel_ind[big[i]]] = color^1;
                continue;
            }
            ans[rel_ind[big[i]]] = color;
            color ^= 1;
        }
        forall(it,rest)
        {
            ans[rel_ind[it]] = ans[rel_ind[parent[it]]]^1;
        }
        rep(i,n) cout << ans[i];
    }
}

• Subtask 1: 0 / 13
• Subtask 2: 0 / 20
• Subtask 3: 0 / 22
• Subtask 4: 19 / 19
• Subtask 5: 0 / 26