#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <vector>
#include <cassert>
typedef long long ll;
const ll INF = 1e17;
const int LEN = 2e5 + 1;
int N;
bool V[LEN];
struct Pos {
int x, y, i;
Pos(int X = 0, int Y = 0, int I = 0) : x(X), y(Y), i(I) {}
ll operator / (const Pos& p) const { return { (ll)x * p.y - (ll)y * p.x }; }
Pos operator - (const Pos& p) const { return { x - p.x, y - p.y }; }
ll Euc() const { return (ll)x * x + (ll)y * y; }
friend std::istream& operator >> (std::istream& is, Pos& p) { is >> p.x >> p.y; return is; }
friend std::ostream& operator << (std::ostream& os, const Pos& p) { os << p.x << " " << p.y; return os; }
}; const Pos O = { 0, 0 };
std::vector<Pos> H;
ll cross(const Pos& d1, const Pos& d2, const Pos& d3) { return (d2 - d1) / (d3 - d2); }
int ccw(const Pos& d1, const Pos& d2, const Pos& d3) {
ll ret = cross(d1, d2, d3);
return !ret ? 0 : ret > 0 ? 1 : -1;
}
ll area(const std::vector<Pos>& H) {
ll ret = 0;
int sz = H.size();
for (int i = 0; i < sz; i++) {
Pos cur = H[i], nxt = H[(i + 1) % sz];
ret += cross(O, cur, nxt);
}
return ret;
}
bool norm(std::vector<Pos>& H) {
ll A = area(H);
assert(A);
if (A > 0) { std::reverse(H.begin(), H.end()); return 1; }
return 0;
}
bool invisible(const Pos& p1, const Pos& p2, const Pos& t) {
return ccw(O, p1, t) <= 0 && ccw(O, p2, t) >= 0 && ccw(p1, p2, t) >= 0;
}
std::vector<int> stack;
void solve() {
std::cin.tie(0)->sync_with_stdio(0);
std::cout.tie(0);
std::cin >> N;
H.resize(N);
for (int i = 0; i < N; i++) std::cin >> H[i], H[i].i = i + 1;
norm(H);//normalize cw
int r = 0, l = 0;
for (int i = 0; i < N; i++) {
if (H[r] / H[i] < 0 || (!(H[r] / H[i]) && H[r].Euc() > H[i].Euc())) r = i;
if (H[l] / H[i] > 0 || (!(H[l] / H[i]) && H[l].Euc() > H[i].Euc())) l = i;
}
stack.clear();
stack.push_back(r);
bool fvis = 1, bvis = 1, rvs = 0;
for (int i = r; i < r + N; i++) {
if (i % N == l) break;
Pos& pre = H[(i - 1 + N) % N], cur = H[i % N], nxt = H[(i + 1) % N];
if (fvis && bvis) {
ll DIR = cur / nxt;
int CCW = ccw(pre, cur, nxt);
if (DIR < 0) {//move backward
if (!rvs && CCW < 0) {
rvs = 1;
fvis = 0;
continue;
}
rvs = 1;
while (stack.size() && invisible(cur, nxt, H[stack.back()])) stack.pop_back();
}
else if (!DIR) {//move vertical
if (cur.Euc() > nxt.Euc()) {
if (stack.size() && stack.back() == i % N) stack.pop_back();
if (stack.size() < 1 || H[stack.back()] / nxt > 0) stack.push_back((i + 1) % N);
}
}
else if (DIR > 0) {//move forward
if (rvs && CCW > 0) {
stack.push_back(i % N);
rvs = 0;
bvis = 0;
continue;
}
if (stack.size() && rvs && H[stack.back()] / cur > 0) stack.push_back(i % N);
rvs = 0;
if (stack.size() < 1 || H[stack.back()] / nxt > 0) stack.push_back((i + 1) % N);
}
}
else if (!fvis) {
if (H[stack.back()] / nxt > 0) {
rvs = 0;
fvis = 1;
stack.push_back((i + 1) % N);
}
}
else if (!bvis) {
if (H[stack.back()] / nxt < 0) {
stack.pop_back();
rvs = 1;
bvis = 1;
while (stack.size() && invisible(cur, nxt, H[stack.back()])) stack.pop_back();
}
}
}
memset(V, 0, sizeof V);
for (const int& i : stack) V[H[i].i] = 1;
std::cout << stack.size() << "\n";
for (int i = 1; i <= N; i++) if (V[i]) std::cout << i << " ";
return;
}
int main() { solve(); return 0; }//boj3303 Printed Circuit Board
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
1 ms |
604 KB |
Output is correct |
| 2 |
Correct |
1 ms |
604 KB |
Output is correct |
| 3 |
Correct |
1 ms |
604 KB |
Output is correct |
| 4 |
Correct |
1 ms |
604 KB |
Output is correct |
| 5 |
Correct |
2 ms |
600 KB |
Output is correct |
| 6 |
Correct |
2 ms |
604 KB |
Output is correct |
| 7 |
Correct |
5 ms |
860 KB |
Output is correct |
| 8 |
Correct |
2 ms |
600 KB |
Output is correct |
| 9 |
Correct |
2 ms |
856 KB |
Output is correct |
| 10 |
Correct |
2 ms |
600 KB |
Output is correct |
| 11 |
Correct |
3 ms |
600 KB |
Output is correct |
| 12 |
Correct |
3 ms |
856 KB |
Output is correct |
| 13 |
Correct |
9 ms |
856 KB |
Output is correct |
| 14 |
Correct |
5 ms |
1116 KB |
Output is correct |
| 15 |
Correct |
7 ms |
1116 KB |
Output is correct |
| 16 |
Correct |
14 ms |
1648 KB |
Output is correct |
| 17 |
Correct |
16 ms |
1624 KB |
Output is correct |
| 18 |
Correct |
26 ms |
2896 KB |
Output is correct |
| 19 |
Correct |
27 ms |
2896 KB |
Output is correct |
| 20 |
Correct |
34 ms |
2828 KB |
Output is correct |
