Submission #500668

#	Time	Username	Problem	Language	Result	Execution time	Memory
500668		rainboy	Wells (CEOI21_wells)	C11	0 / 100	2 ms	288 KiB

wells

#include <stdio.h>
#include <stdlib.h>

#define N	200
#define K	200
#define INF	0x3f3f3f3f
#define MD	1000000007

int max(int a, int b) { return a > b ? a : b; }

int *ej[N], eo[N];

void append(int i, int j) {
	int o = eo[i]++;

	if (o >= 2 && (o & o - 1) == 0)
		ej[i] = (int *) realloc(ej[i], o * 2 * sizeof *ej[i]);
	ej[i][o] = j;
}

int dp[N], dq[N], d_;

void dfs1(int p, int i) {
	int o;

	dp[i] = 1;
	if (p == -1)
		d_ = 0;
	for (o = eo[i]; o--; ) {
		int j = ej[i][o];

		if (j != p) {
			dfs1(i, j);
			if (p == -1)
				d_ = max(d_, dp[i] + dp[j]);
			dp[i] = max(dp[i], dp[j] + 1);
		}
	}
	if (p == -1)
		d_ = max(d_, dp[i]);
}

int dr[N];
char useless[N];

int check(int p, int i, int d, int d_) {
	int o, q1, q2;

	dp[i] = 1, dq[i] = -INF, dr[i] = 1, q1 = q2 = -INF;
	for (o = eo[i]; o--; ) {
		int j = ej[i][o];

		if (j != p) {
			if (!check(i, j, (d + 1) % d_, d_))
				return 0;
			dp[i] = max(dp[i], dp[j] + 1);
			dq[i] = max(dq[i], dq[j]);
			if (d != 0 && dr[i] + dr[j] >= d_)
				return 0;
			dr[i] = max(dr[i], dr[j] + 1);
			if (q1 < dq[j])
				q2 = q1, q1 = dq[j];
			else if (q2 < dq[j])
				q2 = dq[j];
		}
	}
	if (d == 0)
		dq[i] = max(dq[i], dp[i]), dr[i] = 0;
	if (d != 0 && q2 != -INF && (d_ - d) * 2 + 1 <= d_ && (d_ - d) * 2 - 1 + q1 + q2 >= d_)
		return 0;
	return 1;
}

int main() {
	static int qu[N];
	int n, d, h, i, j, k, o, ans, done;

	scanf("%d%d", &n, &d);
	for (i = 0; i < n; i++)
		ej[i] = (int *) malloc(2 * sizeof *ej[i]);
	for (h = 0; h < n - 1; h++) {
		scanf("%d%d", &i, &j), i--, j--;
		append(i, j), append(j, i);
	}
	done = 1;
	for (i = 0; i < n; i++) {
		d_ = 0, dfs1(-1, i);
		if (d_ < d)
			useless[i] = 1;
		else
			done = 0;
		if (dp[i] >= d)
			for (h = 0, j = i; h < d; h++) {
				qu[h] = j;
				for (o = eo[j]; o--; ) {
					k = ej[j][o];
					if (dp[k] == dp[j] - 1) {
						j = k;
						break;
					}
				}
			}
	}
	ans = 1;
	if (!done) {
		ans = 0;
		for (h = 0; h < d; h++)
			if (check(-1, qu[h], 0, d))
				ans++;
		if (ans == 0) {
			printf("NO\n");
			printf("0\n");
			return 0;
		}
	}
	for (i = 0; i < n; i++)
		if (useless[i])
			ans = ans * 2 % MD;
	printf("YES\n");
	printf("%d\n", ans);
	return 0;
}

Compilation message (stderr)

wells.c: In function 'append':
wells.c:16:23: warning: suggest parentheses around '-' in operand of '&' [-Wparentheses]
   16 |  if (o >= 2 && (o & o - 1) == 0)
      |                     ~~^~~
wells.c: In function 'main':
wells.c:78:2: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   78 |  scanf("%d%d", &n, &d);
      |  ^~~~~~~~~~~~~~~~~~~~~
wells.c:82:3: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   82 |   scanf("%d%d", &i, &j), i--, j--;
      |   ^~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 30
• Subtask 2: 0 / 20
• Subtask 3: 0 / 20
• Subtask 4: 0 / 30