Submission #1245064

#	Time	Username	Problem	Language	Result	Execution time	Memory
1245064		Joon_Yorigami	Parking (CEOI22_parking)	C++20	12 / 100	284 ms	69828 KiB

Main

/*
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*/
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vll = vector<ll>;
using sll = set<ll>;
using pll = pair<ll,ll>;

constexpr ll max_n=400010;
ll parent[max_n];
ll sz[max_n];
bool in_cycle[max_n];
ll topcnt[max_n];
ll cnt[max_n];
set<ll> edge[max_n];
vector<pll> moves;
set<ll> available;
bool possible;

ll find(ll x)
{
  if(x==parent[x])
    return x;
  else
    return parent[x] = find(parent[x]);
}

void _union(ll u,ll v)
{
  edge[u].insert(v);
  edge[v].insert(u);
  topcnt[v]+=(u%2)&&(v%2);
  u=find(u);
  v=find(v);
  if(u==v)
    in_cycle[u]=1;
  else
  {
    if(sz[v]>sz[u])
      swap(u,v);
    parent[v]=u;
    sz[u]+=sz[v];
    topcnt[u]+=topcnt[v];
  }
}

void _delete(ll u,ll v)
{
  edge[u].erase(v);
  edge[v].erase(u);
}

ll dfs(ll x)
{
  ll leaf=x;
  stack<ll> stk({x});
  sll seen({x});
  while(!stk.empty())
  {
    ll curr=stk.top();
    stk.pop();
    for(auto neighbour:edge[curr])
    {
      if(seen.find(neighbour)!=seen.end())
        continue;
      seen.insert(neighbour);
      stk.push(neighbour);
      leaf=neighbour;
      break;
    }
  }
  return leaf;
}

void move(ll u,ll v)
{
  moves.push_back({u,v});
  cnt[u]-=1;
  cnt[v]+=1;
  if(cnt[u]==0)
    available.insert(u);
  if(cnt[v]==1)
    available.erase(v);
}

void solve_chain(ll u)
{
  ll curr = dfs(u);
  sll seen({curr});
  vll chain;
  while(curr!=-1)
  {
    chain.push_back(curr);
    ll next = -1;
    for(auto neighbour:edge[curr])
    {
      if(seen.find(neighbour)!=seen.end())
        continue;
      seen.insert(neighbour);
      next=neighbour;
    }
    curr = next;
  }
  ll m=chain.size();
  ll i=0;
  while(i<m)
  {
    ll a=chain[i],b=chain[i+1];
    if(b%2)
    {
      //solvable one move
      move(b/2,a/2);
      i+=2;
      continue;
    }
    ll conflict=-1;
    for(int j=i;j<m-1;j++)
    {
      if(chain[j]%2 && chain[j+1]%2)
      {
        conflict=j;
        break;
      }
    }
    if(conflict==-1)
    {
      //solve all
      for(int j=m-1;j>=i;j-=2)
        move(chain[j-1]/2,chain[j]/2);
      break;
    }
    else
    {
      //need 1 available to open chain
      if(available.size()==0)
      {
        possible=false;
        return;
      }
      ll dump=*available.begin();
      move(chain[conflict]/2,dump);
      move(chain[conflict+1]/2,dump);
      for(int j=conflict-1;j>=i;j-=2)
        move(chain[j-1]/2,chain[j]/2);
      i=conflict+2;
    }
  }
}

void solve_cycle(ll u)
{
  if(available.size()==0)
  {
    possible=false;
    return;
  }
  ll curr = u;
  sll seen({curr});
  vll cycle;
  while(curr!=-1)
  {
    cycle.push_back(curr);
    ll next = -1;
    for(auto neighbour:edge[curr])
    {
      if(seen.find(neighbour)!=seen.end())
        continue;
      seen.insert(neighbour);
      next=neighbour;
    }
    curr = next;
  }
  ll m=cycle.size();
  ll start=0;
  for(int i=0;i<m;i++)
  {
    if(cycle[i]%2)
    {
      start=i;
      if(cycle[(i+1)%m]%2)
        break;
    }
  }
  ll a=cycle[start],b=cycle[(start+1)%m];
  ll dump=*available.begin();
  if(b%2)
  {
    //turn to chain
    move(a/2,dump);
    move(b/2,dump);
    _delete(cycle[(start-1+m)%m],cycle[start]);
    _delete(cycle[start%m],cycle[(start+1)%m]);
    _delete(cycle[(start+1)%m],cycle[(start+2)%m]);
    solve_chain(cycle[(start+2)%m]);
  }
  else
  {
    if(a/2!=b/2)
    {
      move(a/2,dump);
      for(int i=2;i<m;i+=2)
        move(cycle[(start-i+m)%m/2],cycle[(start-i+1+m)%m/2]);
      move(b/2,dump);
    }
    else
    {
      move(a/2,dump);
      for(int i=2;i<m;i+=2)
        move(cycle[(start+i+m)%m/2],cycle[(start+i-1+m)%m/2]);
      move(cycle[(start-1+m)%m]/2,dump);
    }
  }
}

int main()
{
  possible=true;
  ll n,m;
  cin >> n >> m;
  vector<vll> grid(m,vll(2,0));
  vector<vll> idx(n,vll());
  for(int i=0;i<m;i++)
    for(int j=0;j<2;j++)
      cin >> grid[i][j];
  for(int i=0;i<m;i++)
    for(int j=0;j<2;j++)
      grid[i][j]-=1;
  vector<bool> solved(n,false);
  vll row;
  ll top_car,bot_car;
  for(int i=0;i<m;i++)
  {
    parent[i*2]=i*2;
    sz[i*2]=1;
    parent[i*2+1]=i*2+1;
    sz[i*2+1]=1;
    row=grid[i];
    bot_car=row[0];
    top_car=row[1];
    if(bot_car>=0)
    {
      cnt[i]+=1;
      idx[bot_car].push_back(i*2);
    }
    if(top_car>=0)
    {
      cnt[i]+=1;
      idx[top_car].push_back(i*2+1);
    }
    if(bot_car == -1 && top_car==-1)
      available.insert(i);
  }
  for(int i=0;i<n;i++)
  {
    if(idx[i][0]/2!=idx[i][1]/2)
    {
      _union(idx[i][0],idx[i][1]);
    }
  }
  for(int i=0;i<m;i++)
  {
    if(grid[i][1]>=0 && grid[i][0]!=grid[i][1])
      _union(i*2,i*2+1);
  }
  vector<vll> q;
  for(int i=0;i<m*2;i++)
    if(find(i)==i && sz[i]>1)
      q.push_back({in_cycle[i],topcnt[i],i});
  sort(q.begin(),q.end());
  ll start;
  for(auto row:q)
  {
    start=row[2];
    if(row[0])
      solve_cycle(start);
    else
      solve_chain(start);
    if(!possible)
      break;
  }
  if(!possible)
    cout << "-1" << '\n';
  else
  {
    cout << moves.size() << '\n';
    for(auto row:moves)
      cout << row.first+1 << " " << row.second+1 << '\n';
  }
}

• Subtask 1: 2 / 10
• Subtask 2: 10 / 10
• Subtask 3: 0 / 25
• Subtask 4: 0 / 15
• Subtask 5: 0 / 25
• Subtask 6: 0 / 15