Submission #539148

#	Time	Username	Problem	Language	Result	Execution time	Memory
539148		joelau	Planine (COCI21_planine)	C++14	20 / 110	336 ms	32536 KiB

Main

#include <bits/stdc++.h>
using namespace std;
 
long long N,H;
pair<long long,long long> A[1000005];
vector< pair<long double,long double> > lst;
vector<long long> v;
 
int main() {
    ios_base::sync_with_stdio(false); cin.tie(NULL);
    cin >> N >> H;
    for (long long i = 0; i < N; ++i) cin >> A[i].first >> A[i].second;
    for (long long i = 2; i < N-1; i += 2) {
        while (v.size() >= 2 && (A[i-1].second - A[v[v.size()-2]].second) * (A[i-1].first - A[v.back()].first) <= (A[i-1].second - A[v.back()].second) * (A[i-1].first - A[v[v.size()-1]].first))
            v.pop_back();
        v.push_back(i-1);
        long long low = 0, high = v.size();
        while (high - low > 1) {
            long long mid = (low+high)/2;
            if ((A[i].second - A[v[mid-1]].second) * (A[i].first - A[v[mid]].first) <= (A[i].second - A[v[mid]].second) * (A[i].first - A[v[mid-1]].first)) high = mid;
            else low = mid;
        }
        lst.emplace_back(0,A[i].first - (long double) (A[i].first - A[v[low]].first) * (H - A[i].second) / (A[v[low]].second - A[i].second));
    }
    v.clear();
    for (long long i = N-3; i > 0; i -= 2) {
        while (v.size() >= 2 && (A[i+1].second - A[v[v.size()-2]].second) * (A[i+1].first - A[v.back()].first) >= (A[i+1].second - A[v.back()].second) * (A[i+1].first - A[v[v.size()-2]].first))
            v.pop_back();
        v.push_back(i+1);
        long long low = 0, high = v.size();
        while (high - low > 1) {
            long long mid = (low+high)/2;
            if ((A[i].second - A[v[mid-1]].second) * (A[i].first - A[v[mid]].first) >= (A[i].second - A[v[mid]].second) * (A[i].first - A[v[mid-1]].first)) high = mid;
            else low = mid;
        }
        lst[i/2-1].first = A[i].first + (long double) (A[v[low]].first - A[i].first) * (H - A[i].second) / (A[v[low]].second - A[i].second);
    }
    sort(lst.begin(),lst.end());
    long long ans = 0;
    long double n = -1e18;
    for (auto x: lst) if (n < x.second) ans++, n = x.first;
    cout << ans;
 
    return 0;
}

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