Submission #545874

#	Time	Username	Problem	Language	Result	Execution time	Memory
545874		rainboy	Printed Circuit Board (CEOI12_circuit)	C11	85 / 100	171 ms	9184 KiB

circuit

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#define N	200000
 
unsigned int X = 12345;
 
int rand_() {
	return (X *= 3) >> 1;
}
 
long long cross2(int x1, int y1, int x2, int y2) {
	return (long long) x1 * y2 - (long long) x2 * y1;
}
 
int xx[N], yy[N], ii[N * 2];
 
long long cross(int i, int j, int k) {
	return cross2(xx[j] - xx[i], yy[j] - yy[i], xx[k] - xx[i], yy[k] - yy[i]);
}
 
int compare(const void *a, const void *b) {
	int h1 = *(int *) a;
	int h2 = *(int *) b;
	long long c = cross2(xx[ii[h1]], yy[ii[h1]], xx[ii[h2]], yy[ii[h2]]);
 
	return c ? (c < 0 ? -1 : 1) : (h1 & 1) - (h2 & 1);
}
 
int iq[1 + N], pq[N], cnt, x_, y_;
 
double t(int i, int j) {
	return (double) cross2(xx[i], yy[i], xx[j] - xx[i], yy[j] - yy[i]) / cross2(x_, y_, xx[j] - xx[i], yy[j] - yy[i]);
}
 
int lt(int i, int j) {
	double t1 = t(ii[i << 1 | 0], ii[i << 1 | 1]), t2 = t(ii[j << 1 | 0], ii[j << 1 | 1]);
 
	if (t1 != t2)
		return t1 < t2;
	return cross(ii[i << 1 | 0], ii[j << 1 | 0], ii[j << 1 | 1]) < 0 || cross(ii[i << 1 | 1], ii[j << 1 | 0], ii[j << 1 | 1]) < 0;
}
 
int p2(int p) {
	return (p *= 2) > cnt ? 0 : (p < cnt && lt(iq[p + 1], iq[p]) ? p + 1 : p);
}
 
void pq_up(int i) {
	int p, q, j;
 
	for (p = pq[i]; (q = p / 2) && lt(i, j = iq[q]); p = q)
		iq[pq[j] = p] = j;
	iq[pq[i] = p] = i;
}
 
void pq_dn(int i) {
	int p, q, j;
 
	for (p = pq[i]; (q = p2(p)) && lt(j = iq[q], i); p = q)
		iq[pq[j] = p] = j;
	iq[pq[i] = p] = i;
}
 
void pq_add(int i) {
	pq[i] = ++cnt, pq_up(i);
}
 
void pq_remove(int i) {
	if (pq[i]) {
		int j = iq[cnt--];
 
		if (j != i)
			pq[j] = pq[i], pq_up(j), pq_dn(j);
		pq[i] = 0;
	}
}
 
int main() {
	static int hh[N * 2];
	static char visible[N];
	int n, n_, g, h, h_, i;
 
	scanf("%d", &n);
	for (i = 0; i < n; i++)
		scanf("%d%d", &xx[i], &yy[i]);
	n_ = 0;
	for (i = 0; i < n; i++) {
		long long c = cross2(xx[i], yy[i], xx[(i + 1) % n], yy[(i + 1) % n]);
 
		if (c < 0) {
			ii[i << 1 | 0] = i, ii[i << 1 | 1] = (i + 1) % n;
			hh[n_++] = i << 1 | 0, hh[n_++] = i << 1 | 1;
		} else if (c > 0) {
			ii[i << 1 | 0] = (i + 1) % n, ii[i << 1 | 1] = i;
			hh[n_++] = i << 1 | 0, hh[n_++] = i << 1 | 1;
		}
	}
	qsort(hh, n_, sizeof *hh, compare);
	memset(visible, 1, n * sizeof *visible);
	for (h = 0; h < n_; h++) {
		h_ = hh[h];
		x_ = xx[ii[h_]], y_ = yy[ii[h_]];
		if ((h_ & 1) == 0)
			pq_add(h_ >> 1);
		else
			pq_remove(h_ >> 1);
		if (cnt) {
			i = iq[1];
			if (cross(ii[i << 1 | 0], ii[i << 1 | 1], ii[h_]) > 0)
				visible[ii[h_]] = 0;
		}
	}
	for (h = 0; h < n_; h = h_) {
		int h1, i_;
 
		h1 = hh[h], h_ = h, i_ = -1;
		while (h_ < n_ && cross2(xx[ii[h1]], yy[ii[h1]], xx[ii[hh[h_]]], yy[ii[hh[h_]]]) == 0) {
			i = ii[hh[h_++]];
			if (i_ == -1 || xx[i_] > xx[i])
				i_ = i;
		}
		for (g = h; g < h_; g++) {
			i = ii[hh[g]];
			if (i != i_)
				visible[i] = 0;
		}
	}
	cnt = 0;
	for (i = 0; i < n; i++)
		if (visible[i])
			cnt++;
	printf("%d\n", cnt);
	for (i = 0; i < n; i++)
		if (visible[i])
			printf("%d ", i + 1);
	printf("\n");
	return 0;
}

Compilation message (stderr)

circuit.c: In function 'main':
circuit.c:84:2: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   84 |  scanf("%d", &n);
      |  ^~~~~~~~~~~~~~~
circuit.c:86:3: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   86 |   scanf("%d%d", &xx[i], &yy[i]);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 85 / 100