Submission #1079497

#	Time	Username	Problem	Language	Result	Execution time	Memory
1079497		LittleOrange	Radio Towers (IOI22_towers)	C++17	56 / 100	721 ms	4552 KiB

towers

#include "towers.h"

#include <vector>
#include<bits/stdc++.h>
using namespace std;
using ll = int;
const ll big = 1e9+10;
ll n;
vector<ll> h,lh,rh;
//ll mx;
vector<ll> ps;
vector<pair<ll,ll>> rgs;
struct obj{
  ll v,c;
  bool operator<(const obj &o) const{
    return v<o.v;
  }
  bool operator>(const obj &o) const{
    return v>o.v;
  }
};

void init(int N, std::vector<int> H) {
  n = N;
  h = H;
  //for(ll i = 0;i<n;i++) if((i==0||(h[i-1]<h[i]))&&(i==n-1||h[i]>h[i+1])) mx = i;
  //for(ll i = 1;i<n-1;i++){
  //  if (h[i-1]<h[i]&&h[i]>h[i+1]){
  //    ps.push_back(i);
  //  }
  //}
  //for(auto [u,v] : ps) cerr << "[" << u << "," << v << "]" << " ";cerr << "\n";
  lh.resize(n,0);
  rh.resize(n,0);
  {
    vector<pair<ll,ll>> v;
    v.push_back({h[0],h[0]});
    for(ll i = 1;i<n;i++){
      ll mi = h[i];
      while(v.size()&&v.back().first<h[i]){
        mi = min(mi,v.back().second);
        v.pop_back();
      }
      lh[i] = h[i]-mi;
      v.push_back({h[i],mi});
    }
  }
  {
    vector<pair<ll,ll>> v;
    v.push_back({h[n-1],h[n-1]});
    for(ll i = n-2;i>=0;i--){
      ll mi = h[i];
      while(v.size()&&v.back().first<h[i]){
        mi = min(mi,v.back().second);
        v.pop_back();
      }
      rh[i] = h[i]-mi;
      v.push_back({h[i],mi});
    }
  }
}
bool ps_inited = false;
void init_ps(ll d){
  ps_inited = true;
  vector<ll> ld(n,big),rd(n,big);
  {
    vector<pair<ll,ll>> v;
    v.push_back({h[0],0});
    for(ll i = 1;i<n;i++){
      auto it = lower_bound(v.begin(),v.end(),make_pair(h[i]-d+1,0));
      if (it!=v.begin()) ld[i] = i-(*--it).second;
      while(v.size()&&v.back().first>h[i]) v.pop_back();
      v.push_back({h[i],i});
    }
  }
  {
    vector<pair<ll,ll>> v;
    v.push_back({h[n-1],n-1});
    for(ll i = n-2;i>=0;i--){
      auto it = lower_bound(v.begin(),v.end(),make_pair(h[i]-d+1,0));
      if (it!=v.begin()) rd[i] = (*--it).second-i;
      while(v.size()&&v.back().first>h[i]) v.pop_back();
      v.push_back({h[i],i});
    }
  }
  for(ll i = 0;i<n;i++) if(lh[i]>=d&&rh[i]>=d) {
    ps.push_back(i);
    rgs.push_back({i-ld[i],i+rd[i]});
    //cerr << i-ld[i] << " " << i << " " << i+rd[i] << "\n";
  }
}

int max_towers(int L, int R, int D) {
  if(!ps_inited) init_ps(D);
  ll l = L, r = R, d = D;
  ll ans = 1;
  //auto it0 = lower_bound(ps.begin(),ps.end(),r);
  //ll rf = it0-ps.begin();
  //auto it1 = lower_bound(ps.begin(),ps.end(),l+1);
  //ll lf = it1-ps.begin();
  //cerr << lf << " " << rf << "\n";
  //ans = max(0,rf-lf)+1;
  auto it0 = lower_bound(rgs.begin(),rgs.end(),make_pair(r,0));
  //if (it0!=rgs.begin()) --it0;
  ll rf = it0-rgs.begin();
  if (it0!=rgs.begin()){
    if ((*--it0).second>r) --rf;
  }
  auto it1 = lower_bound(rgs.begin(),rgs.end(),make_pair(l,0));
  ll lf = it1-rgs.begin();
  ans = max(0,rf-lf)+1;
  return ans;
  /*vector<obj> a,b;
  a.push_back({0,0});
  b.push_back({big,0});
  for(ll i = l;i<=r;i++){
    ll cur = 0;
    auto it = lower_bound(b.begin(),b.end(),obj({h[i]-1,0}),greater<obj>());
    --it;
    cur = (*it).c;
    ans = max(ans,cur+1);
    obj oa = {h[i],cur+1};
    if (a.size()<=oa.c) a.push_back(oa);
    else a[oa.c] = min(a[oa.c],oa);
    auto it0 = lower_bound(a.begin(),a.end(),obj({h[i]-d+1,0}));
    --it0;
    obj ob = {h[i]-d,(*it0).c};
    if (b.size()<=ob.c) b.push_back(ob);
    else b[ob.c] = max(b[ob.c],ob);
    ans = max(ans,cur+1);
    //cerr << "a:";for(auto [u,v] : a) cerr << "(" << u <<"," << v << ") ";cerr << "\n";
    //cerr << "b:";for(auto [u,v] : b) cerr << "(" << u <<"," << v << ") ";cerr << "\n";
  }*/
  return ans;
}

Compilation message (stderr)

towers.cpp: In function 'int max_towers(int, int, int)':
towers.cpp:95:20: warning: unused variable 'd' [-Wunused-variable]
   95 |   ll l = L, r = R, d = D;
      |                    ^

• Subtask 1: 0 / 4
• Subtask 2: 11 / 11
• Subtask 3: 12 / 12
• Subtask 4: 14 / 14
• Subtask 5: 0 / 17
• Subtask 6: 19 / 19
• Subtask 7: 0 / 23