Submission #588032

#	Time	Username	Problem	Language	Result	Execution time	Memory
588032		MilosMilutinovic	Planine (COCI21_planine)	C++14	0 / 110	4 ms	852 KiB

Main

/**
 *    author:  wxhtzdy
 *    created: 02.07.2022 16:49:56
**/
#include <bits/stdc++.h>

using namespace std;

#define int long long

signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);  
  int n, h;
  cin >> n >> h;
  vector<int> x(n), y(n);
  for (int i = 0; i < n; i++) {
    cin >> x[i] >> y[i];
  }              
  vector<pair<int, int>> ev;
  for (int i = 2; i < n - 1; i += 2) {
    ev.emplace_back(i, 0);
    ev.emplace_back(i, 1);
  }
  sort(ev.begin(), ev.end(), [&](pair<int, int> a, pair<int, int> b) {
    int xa = x[a.first];
    int xb = x[b.first];
    int pa = (a.second == 0 ? x[a.first - 1] : x[a.first + 1]) - x[a.first];
    int pb = (b.second == 0 ? x[b.first - 1] : x[b.first + 1]) - x[b.first];
    int qa = (a.second == 0 ? y[a.first - 1] : y[a.first + 1]) - y[a.first];
    int qb = (b.second == 0 ? y[b.first - 1] : y[b.first + 1]) - y[b.first];
    double new_xa = xa + h * ((double) pa / (double) qa);
    double new_xb = xb + h * ((double) pb / (double) qb);
    
    // xa + h * (pa / qa) < xb + h * (pb / qb)
    // xa - xb < h * (pb / qb - pa / qa)
    // (xa - xb) / h < pb / qb - pa / qa
    // (xa - xb) / h < (pb * qa - pa * qb) / qa * qb
    // (xa - xb) * (qa * qb) < (pb * qa - pa * qb) * h
    long long dx = xa - xb;
    long long pq = qa * 1LL * qb;
    long long qp = pb * 1LL * qa - pa * 1LL * qb;
    long long L = dx * pq;
    long long R = qp * h;
    if (new_xa == new_xb) {
      return a.second < b.second;  
    } else {
      return new_xa < new_xb;
    }         
   });              
  int ans = 0;
  set<int> alive;    
  for (auto& e : ev) {
    if (e.second == 0) {
      alive.insert(e.first);
    } else {   
      if (alive.find(e.first) == alive.end()) {
        continue;
      }
      alive.clear();
      ans += 1;
    }
  }
  cout << ans << '\n';
  return 0;
}

Compilation message (stderr)

Main.cpp: In lambda function:
Main.cpp:43:15: warning: unused variable 'L' [-Wunused-variable]
   43 |     long long L = dx * pq;
      |               ^
Main.cpp:44:15: warning: unused variable 'R' [-Wunused-variable]
   44 |     long long R = qp * h;
      |               ^

• Subtask 1: 0 / 20
• Subtask 2: 0 / 30
• Subtask 3: 0 / 60