답안 #120331

# 제출 시각 아이디 문제 언어 결과 실행 시간 메모리
120331 2019-06-24T08:17:48 Z tmwilliamlin168 Printed Circuit Board (CEOI12_circuit) C++14
100 / 100
46 ms 4724 KB
#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);
	s={0, 1};
	for(int i=2; i<v.size(); ++i) {
		auto escapeRightLeft=[&]() {
			//c set to if i is hidden by s.back()
			int j=i, c=cp(n, v[s.back()], v[i])<0;
			//while i is not to the right of s.back() or i is hidden by segment j
			while(cp(n, v[s.back()], v[i])>=0||!c) {
				//if this is the first side, c will be one iff the new edge goes forwards and is not hidden by segment j
				if(i==j)
					c=cp(n, v[i], v[i+1])<0&&cp(v[i-1], v[i], v[i+1])>0;
				//if we start not to the right of j but end up to the right of j and j does not hide i+1
				if(cp(n, v[j], v[i])>=0&&cp(n, v[j], v[i+1])<0&&cp(v[i], v[i+1], v[j])>0)
					++c;
				//if we start to the right of j but end up not to the right of j and j does not hide i+1
				if(cp(n, v[j], v[i])<0&&cp(n, v[j], v[i+1])>=0&&cp(v[i], v[i+1], v[j])<0)
					--c;
				++i;
			}
		};
		//side going strictly forwards
		if(cp(n, v[i-1], v[i])<0) {
			//last side went strictly backwards and current side is now hidden
			if(cp(n, v[i-2], v[i-1])>0&&cp(v[i-2], v[i-1], v[i])<0) {
				//while hidden
				while(cp(n, v[s.back()], v[i])<=0)
					++i;
				s.pop_back();
				//while one of s.back() and i hides the other and it is actually s.back() which is hidden 
				while(cp(n, v[s.back()], v[i])>=0&&cp(v[i-1], v[i], v[s.back()])<0)
					s.pop_back();
				escapeRightLeft();
			}
		}
		//side going strictly backwards
		else if(cp(n, v[i-1], v[i])>0) {
			//last side went strictly forwards and current side is now hidden
			if(cp(n, v[i-2], v[i-1])<0&&cp(v[i-2], v[i-1], v[i])>0) {
				//while hidden
				while(cp(n, v[s.back()], v[i])>=0)
					++i;
			} else {
				//while one of s.back() and i hides the other and it is actually s.back() which is hidden
				//note <= here so we can pop off v[i-1]
				while(cp(n, v[s.back()], v[i])>=0&&cp(v[i-1], v[i], v[s.back()])<=0)
					s.pop_back();
				escapeRightLeft();
			}
		}
		//side not changing angle
		else {
			//if new point hides old point
			if((cp(n, v[i-2], v[i-1])<0)==(cp(v[i-2], v[i-1], v[i])<0))
				s.pop_back();
			//last side went strictly forwards and current side is now hidden
			else if(cp(n, v[i-2], v[i-1])<0) {
				//while hidden
				while(cp(n, v[s.back()], v[i])>=0)
					++i;
			}
			//last side went strictly backwards and current side is now hidden
			else {
				//while hidden
				while(cp(n, v[s.back()], v[i])<=0)
					++i;
				s.pop_back();
				//while one of s.back() and i hides the other and it is actually s.back() which is hidden 
				while(cp(n, v[s.back()], v[i])>=0&&cp(v[i-1], v[i], v[s.back()])<0)
					s.pop_back();
				escapeRightLeft();
			}
		}
		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

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:33:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=2; i<v.size(); ++i) {
               ~^~~~~~~~~
# 결과 실행 시간 메모리 Grader output
1 Correct 2 ms 384 KB Output is correct
2 Correct 2 ms 384 KB Output is correct
3 Correct 3 ms 512 KB Output is correct
4 Correct 3 ms 512 KB Output is correct
5 Correct 4 ms 640 KB Output is correct
6 Correct 13 ms 640 KB Output is correct
7 Correct 6 ms 896 KB Output is correct
8 Correct 3 ms 568 KB Output is correct
9 Correct 4 ms 640 KB Output is correct
10 Correct 4 ms 640 KB Output is correct
11 Correct 5 ms 640 KB Output is correct
12 Correct 6 ms 768 KB Output is correct
13 Correct 9 ms 1024 KB Output is correct
14 Correct 9 ms 1280 KB Output is correct
15 Correct 12 ms 1664 KB Output is correct
16 Correct 21 ms 2560 KB Output is correct
17 Correct 23 ms 2296 KB Output is correct
18 Correct 40 ms 4724 KB Output is correct
19 Correct 43 ms 4596 KB Output is correct
20 Correct 46 ms 4724 KB Output is correct