Submission #949042

#	Time	Username	Problem	Language	Result	Execution time	Memory
949042		rainboy	초록색 삼각형 (YDX13_green)	C11	1 / 1	629 ms	600 KiB

C

#include <stdio.h>

#define N	2000

typedef __int128_t L;

unsigned int Z = 12345;

int rand_() {
	return (Z *= 3) >> 1;
}

int xx[N], yy[N];

long long cross2(int i, int j) {
	return (long long) xx[i] * yy[j] - (long long) xx[j] * yy[i];
}

long long cross(int i, int j, int k) {
	return (long long) (xx[j] - xx[i]) * (yy[k] - yy[i]) - (long long) (xx[k] - xx[i]) * (yy[j] - yy[i]);
}

int o;

int compare(int i, int j) {
	int sgni, sgnj;
	long long c;

	sgni = xx[i] < xx[o] || xx[i] == xx[o] && yy[i] < yy[o] ? -1 : 1;
	sgnj = xx[j] < xx[o] || xx[j] == xx[o] && yy[j] < yy[o] ? -1 : 1;
	if (sgni != sgnj)
		return sgni - sgnj;
	c = cross(o, i, j);
	return c == 0 ? 0 : (c < 0 ? -1 : 1);
}

void sort(int *jj, int l, int r) {
	while (l < r) {
		int i = l, j = l, k = r, j_ = jj[l + rand_() % (r - l)], tmp;

		while (j < k) {
			int c = compare(jj[j], j_);

			if (c == 0)
				j++;
			else if (c < 0) {
				tmp = jj[i], jj[i] = jj[j], jj[j] = tmp;
				i++, j++;
			} else {
				k--;
				tmp = jj[j], jj[j] = jj[k], jj[k] = tmp;
			}
		}
		sort(jj, l, i);
		l = k;
	}
}

int main() {
	static int jj[N];
	int n, n_, i, j, k;
	L ans;

	scanf("%d", &n);
	if (n <= 2) {
		printf("0\n");
		return 0;
	}
	for (i = 0; i < n; i++)
		scanf("%d%d", &xx[i], &yy[i]);
	ans = 0;
	for (i = 0; i < n; i++) {
		n_ = 0;
		for (j = 0; j < n; j++)
			if (j != i)
				jj[n_++] = j;
		o = i, sort(jj, 0, n_);
		for (j = 0, k = 0; j < n_; j++) {
			while (k < j + n_ && cross(o, jj[j % n_], jj[k % n_]) <= 0)
				k++;
			ans += (L) (k - j - 1) * cross2(jj[j % n_], o);
		}
	}
	printf("%.12f\n", (double) ans / 2 / ((long long) n * (n - 1) * (n - 2) / 6));
	return 0;
}

Compilation message (stderr)

C.c: In function 'compare':
C.c:29:41: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   29 |  sgni = xx[i] < xx[o] || xx[i] == xx[o] && yy[i] < yy[o] ? -1 : 1;
      |                          ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~
C.c:30:41: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   30 |  sgnj = xx[j] < xx[o] || xx[j] == xx[o] && yy[j] < yy[o] ? -1 : 1;
      |                          ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~
C.c: In function 'main':
C.c:64:2: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   64 |  scanf("%d", &n);
      |  ^~~~~~~~~~~~~~~
C.c:70:3: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   70 |   scanf("%d%d", &xx[i], &yy[i]);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 1 / 1