Submission #490932

#	Time	Username	Problem	Language	Result	Execution time	Memory
490932		rainboy	Ljetopica (COI19_ljetopica)	C11	39 / 100	67 ms	300 KiB

ljetopica

#include <stdio.h>
#include <string.h>

#define N	1000
#define MD	1000000007

int pp2[N + 1], vv[N + 1], ff[N + 1], gg[N + 1];

void init() {
	int i;

	pp2[0] = 1;
	for (i = 1; i <= N; i++)
		pp2[i] = pp2[i - 1] * 2 % MD;
	ff[0] = gg[0] = 1;
	for (i = 1; i <= N; i++) {
		vv[i] = i == 1 ? 1 : (long long) vv[i - MD % i] * (MD / i + 1) % MD;
		ff[i] = (long long) ff[i - 1] * i % MD;
		gg[i] = (long long) gg[i - 1] * vv[i] % MD;
	}
}

int choose(int n, int k) {
	return (long long) ff[n] * gg[k] % MD * gg[n - k] % MD;
}

int ans;

void brute(int n, int i, int k, int x, int l, int r) {
	if (k == 0) {
		if (l <= x && x <= r)
			ans = (ans + x) % MD;
		x ^= (1 << n - 1) - 1;
		if (l <= x && x <= r)
			ans = (ans + x) % MD;
		return;
	}
	while (i < n - 1)
		brute(n, i + 1, k - 1, x ^ (1 << n - 1 - i) - 1, l, r), i++;
}

int main() {
	static char cc[N + 1], aa[N + 1], bb[N + 1];
	int n, k, i, l, r, x;

	init();
	scanf("%d%d%s%s%s", &n, &k, cc, aa, bb);
	if (n <= 25) {
		l = 0;
		for (i = 0; i < n; i++)
			l = l * 2 + aa[i] - '0';
		r = 0;
		for (i = 0; i < n; i++)
			r = r * 2 + bb[i] - '0';
		x = 1;
		for (i = 0; i < n - 1; i++)
			x = x * 2 + (cc[i] == 'L' ? 0 : 1);
		ans = 0;
		brute(n, 0, k, x, l, r);
		printf("%d\n", ans);
		return 0;
	}
	if (k == 0 && strcmp(aa, bb) == 0) {
		ans = 0;
		for (i = 0; i < n; i++)
			ans = (ans * 2 + aa[i] - '0') % MD;
		printf("%d\n", ans);
		return 0;
	}
	printf("%lld\n", (long long) (pp2[n - 1] + pp2[n] - 1) % MD * choose(n - 1, k) % MD);
	return 0;
}

Compilation message (stderr)

ljetopica.c: In function 'brute':
ljetopica.c:33:16: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
   33 |   x ^= (1 << n - 1) - 1;
      |              ~~^~~
ljetopica.c:39:42: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
   39 |   brute(n, i + 1, k - 1, x ^ (1 << n - 1 - i) - 1, l, r), i++;
      |                                    ~~~~~~^~~
ljetopica.c:39:47: warning: suggest parentheses around arithmetic in operand of '^' [-Wparentheses]
   39 |   brute(n, i + 1, k - 1, x ^ (1 << n - 1 - i) - 1, l, r), i++;
      |                              ~~~~~~~~~~~~~~~~~^~~
ljetopica.c: In function 'main':
ljetopica.c:47:2: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   47 |  scanf("%d%d%s%s%s", &n, &k, cc, aa, bb);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 8 / 8
• Subtask 2: 14 / 14
• Subtask 3: 17 / 17
• Subtask 4: 0 / 61