Submission #119646

#	Time	Username	Problem	Language	Result	Execution time	Memory
119646		tmwilliamlin168	Printed Circuit Board (CEOI12_circuit)	C++14	20 / 100	53 ms	6132 KiB

circuit

#include <bits/stdc++.h>
using namespace std;

#define ll long long

const int mxN=2e5;
int n, l, r;
ll x[mxN+1], y[mxN+1];
vector<int> v, s;
bool b[mxN];

ll cp(int a, int b, int c) {
	return (y[c]-y[a])*(x[b]-x[a])-(y[b]-y[a])*(x[c]-x[a]);
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n;
	for(int i=0; i<n; ++i) {
		cin >> x[i] >> y[i];
		if(!i||cp(n, l, i)>0||!cp(n, l, i)&&x[i]<x[l])
			l=i;
		if(!i||cp(n, r, i)<0||!cp(n, r, i)&&x[i]<x[r])
			r=i;
	}
	int ic=cp((l+n-1)%n, l, (l+1)%n)>0?1:n-1;
	for(; l^r; l=(l+ic)%n)
		v.push_back(l);
	v.push_back(r);
	//cout << "a" << endl;
	//for(int i : v)
		//cout << x[i] << " " << y[i] << endl;
	s={0, 1};
	for(int i=2; i<v.size(); ++i) {
		//cout << i << endl;
		//for(int si : s)
			//cout << si << " ";
		//cout << endl;
		if(cp(n, v[i-1], v[i])<0) {
			if((cp(n, v[s.back()-1], v[s.back()])<=0||cp(v[s.back()-1], v[s.back()], v[i])>0)&&cp(n, v[s.back()], v[i])<0)
				s.push_back(i);
		} else {
			if(s.back()==i-1) {
				if(cp(n, v[i-2], v[i-1])<0&&cp(v[i-2], v[i-1], v[i])>0)
					continue;
				s.pop_back();
			} else if(s.back()&&cp(n, v[s.back()-1], v[s.back()])>=0) {
				if(cp(n, v[s.back()], v[i])<=0)
					continue;
				s.pop_back();
			}
			while(cp(n, v[i], v[s.back()])<=0&&cp(v[i], v[i-1], v[s.back()])>0)
				s.pop_back();
			if(cp(n, v[i], v[s.back()])>0)
				s.push_back(i);
		}
	}
	cout << s.size() << "\n";
	for(int a : s)
		b[v[a]]=1;
	for(int i=0; i<n; ++i)
		if(b[i])
			cout << i+1 << " ";
}

Compilation message (stderr)

circuit.cpp: In function 'int main()':
circuit.cpp:23:37: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   if(!i||cp(n, l, i)>0||!cp(n, l, i)&&x[i]<x[l])
                         ~~~~~~~~~~~~^~~~~~~~~~~
circuit.cpp:25:37: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   if(!i||cp(n, r, i)<0||!cp(n, r, i)&&x[i]<x[r])
                         ~~~~~~~~~~~~^~~~~~~~~~~
circuit.cpp:36:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=2; i<v.size(); ++i) {
               ~^~~~~~~~~

• Subtask 1: 20 / 100