Submission #119657

#	Time	Username	Problem	Language	Result	Execution time	Memory
119657		Milki	Alternating Current (BOI18_alternating)	C++14	19 / 100	134 ms	8208 KiB

alternating

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

#define FOR(i, a, b) for(int i = a; i < b; ++i)
#define REP(i, n) FOR(i, 0, n)
#define _ << " " <<
#define sz(x) ((int) x.size())
#define pb(x) push_back(x)
#define TRACE(x) cerr << #x << " = " << x << endl

typedef long long ll;
typedef pair<int, int> point;

const int MAXN = 1e5 + 5, off = 1 << 17;

struct event{
  int x, y, id;
  event(){}
  event(int x, int y, int id) : x(x), y(y), id(id) {}

  friend bool operator < (const event &A, const event &B){
    if(A.x != B.x) return A.x < B.x;
    return A.y > B.y;
  }
};

int n, m, par[MAXN];
event rail[MAXN];
vector <event> v, ev;
bool sol[MAXN];

struct Tournament{
  int t[2 * off], p[2 * off];

  Tournament(){}
  void reset(){
    memset(t, 0, sizeof(t));
    memset(p, 0, sizeof(p));
  }
  void prop(int x){
    if(!t[x])
      t[x] = p[x];
    if(x < off){
      p[x * 2] = max(p[x], p[x * 2]);
      p[x * 2 + 1] = max(p[x], p[x * 2 + 1]);
    }
    p[x] = 0;
  }
  void update(int x, int lo, int hi, int a, int b){
    prop(x);
    if(lo >= b || hi <= a) return;
    if(lo >= a && hi <= b) { p[x] = 1; prop(x); return; }
    int mid = (lo + hi) >> 1;
    update(x * 2, lo, mid, a, b); update(x * 2 + 1, mid, hi, a, b);
  }
  int get(int x, int lo, int hi, int a, int b){
    prop(x);
    if(lo >= b || hi <= a) return 0;
    if(lo >= a && hi <= b) return t[x];
    int mid = (lo + hi) >> 1;
    return get(x * 2, lo, mid, a, b) +
           get(x * 2 + 1, mid, hi, a, b);
  }

} T;

bool check(int x){
  T.reset();
  REP(i, m){
    if(sol[i] == x){
      if(rail[i].x > rail[i].y){
        T.update(1, 0, off, rail[i].x, n + 1);
        T.update(1, 0, off, 1, rail[i].y + 1);
      }
      else{
        T.update(1, 0, off, rail[i].x, rail[i].y + 1);
      }
    }
  }
  int sum = 0;
  REP(i, n)
    sum += T.get(1, 0, off, i + 1, i + 2);

  if(sum == n)
    return true;
  else
    return false;
}

int parent[MAXN];

int f(int x){
  if(parent[x] == x) return x;
  return par[x] = f(par[x]);
}

void spoji(int x, int y){
  x = f(x); y = f(y);
  if(x == y) return;
  parent[y] = x;
}

int main(){
  ios_base::sync_with_stdio(false); cin.tie(0);
  memset(par, -1, sizeof(par));

  cin >> n >> m;
  REP(i, m){
    int a, b; cin >> a >> b;
    rail[i] = event(a, b, i);
    parent[i] = i;

    if(a <= b)
      v.pb(event(a, b, i));
    if(a > b)
      v.pb(event(a, b + n, i));
    else
      v.pb(event(a + n, b + n, i));
  }
  sort(v.begin(), v.end());

  event curr = v[0];
  FOR(i, 1, sz(v)){
    if(curr.x <= v[i].x && curr.y >= v[i].y){
      par[ v[i].id ] = curr.id;
      spoji(curr.id, v[i].id);
    }

    if(curr.y < v[i].y)
      curr = v[i];
  }

  REP(i, m)
    if(f(i) == i)
      ev.pb(rail[i]);
  sort(ev.begin(), ev.end());

  for(int i = 0; i < sz(ev); i += 2)
    sol[ ev[i].id ] = true;
  REP(i, m){
    if(f(i) != i)
      sol[i] = !sol[ f(i) ] ;
  }

  if(check(0) && check(1))
    REP(i, m)
      cout << sol[i];
  else
    cout << "impossible";
}

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