Submission #537723

#	Time	Username	Problem	Language	Result	Execution time	Memory
537723		jamezzz	Planine (COCI21_planine)	C++17	110 / 110	397 ms	56992 KiB

Main

#include <bits/stdc++.h>
using namespace std;
 
#define sf scanf
#define pf printf
#define fi first
#define se second
#define pb push_back
#define sz(x) (int)x.size()
#define all(x) x.begin(),x.end()
#define INF 1023456789
typedef long long ll;
typedef long double ld;
typedef pair<ld,ld> ii;

#define maxn 1000005
 
int n,h,x[maxn],y[maxn],px[maxn],py[maxn],nx[maxn],ny[maxn];
 
struct line{
	ll x1,x2,y1,y2;
	int cross(line &o){//where does this line intersect
		ll x3=o.x1,x4=o.x2,y3=o.y1,y4=o.y2;
		if((x1-x2)*(y3-y4)==(x3-x4)*(y1-y2))return 2;//parallel
		ll num=(y3-y4)*(y1*(x1-x2)-x1*(y1-y2))-(y1-y2)*(y3*(x3-x4)-x3*(y3-y4));
		ll den=(y3-y4)*(x1-x2)-(y1-y2)*(x3-x4);
		if(num==h*den)return 0;//intersect exactly
		if((den>0&&num<h*den)||(den<0&&num>h*den))return -1;//intersect below
		if((den>0&&num>h*den)||(den<0&&num<h*den))return 1;//intersect above
	}
	bool cmp(line &o){
		ll a=x2-x1,b=y2-y1,c=o.x2-o.x1,d=o.y2-o.y1;
		if(x1<o.x1){
			if(b*c>d*a)return true;//intersect below
			if(cross(o)<=0)return false;
			else return true;
		}
		else{
			if(b*c<d*a)return false;//intersect below
			if(cross(o)==-1)return true;
			else return false;
		}
	}
};
 
struct valley{
	line l1,l2;
};

vector<valley> r;
vector<int> hull;
 
int main(){
	sf("%d%d",&n,&h);
	for(int i=1;i<=n;++i)sf("%d%d",&x[i],&y[i]);
	hull.pb(1);
	for(int i=1;i<=n;++i){
		while(sz(hull)>=2){
			int a=hull[sz(hull)-2],b=hull.back();
			int x1=x[a],y1=y[a],x2=x[b],y2=y[b],x3=x[i],y3=y[i];
			if((ll)(y2-y1)*(x3-x2)<=(ll)(y3-y2)*(x2-x1))hull.pop_back();
			else break;
		}
		int a=hull.back();
		px[i]=x[a],py[i]=y[a];
		hull.push_back(i);
	}
	while(!hull.empty())hull.pop_back();
	hull.pb(n);
	for(int i=n;i>=1;--i){
		while(sz(hull)>=2){
			int a=hull[sz(hull)-2],b=hull.back();
			int x1=x[a],y1=y[a],x2=x[b],y2=y[b],x3=x[i],y3=y[i];
			if((ll)(y1-y2)*(x2-x3)>=(ll)(y2-y3)*(x1-x2))hull.pop_back();
			else break;
		}
		int a=hull.back();
		nx[i]=x[a],ny[i]=y[a];
		hull.push_back(i);
	}
	for(int i=3;i<n;i+=2){
		line l1={x[i],px[i],y[i],py[i]};
		line l2={x[i],nx[i],y[i],ny[i]};
		r.pb({l1,l2});
	}
	sort(all(r),[](valley &a,valley &b){
		return a.l2.cmp(b.l2);
	});
	int ans=0;
	line pv=r[0].l1;
	pv.x1-=1;pv.x2-=1;
	for(int i=0;i<sz(r);++i){
		if(pv.cross(r[i].l1)>=1){
			++ans;pv=r[i].l2;
		}
	}
	pf("%d\n",ans);
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:54:4: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   54 |  sf("%d%d",&n,&h);
      |    ^
Main.cpp:55:25: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   55 |  for(int i=1;i<=n;++i)sf("%d%d",&x[i],&y[i]);
      |                         ^
Main.cpp: In member function 'int line::cross(line&)':
Main.cpp:30:2: warning: control reaches end of non-void function [-Wreturn-type]
   30 |  }
      |  ^

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