Submission #494170

#	Time	Username	Problem	Language	Result	Execution time	Memory
494170		rainboy	Newspapers (CEOI21_newspapers)	C11	100 / 100	1 ms	332 KiB

newspapers

/* https://csacademy.com/contest/archive/task/catch-the-thief */
#include <stdio.h>
#include <stdlib.h>

#define N	1000

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 pp[N], i_, d_;

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

	pp[i] = p;
	if (d_ < d)
		i_ = i, d_ = d;
	for (o = eo[i]; o--; ) {
		int j = ej[i][o];

		if (j != p)
			dfs1(i, j, d + 1);
	}
}

char path[N];

int dfs2(int p, int i, int d) {
	int o;

	if (d >= 3)
		return 0;
	for (o = eo[i]; o--; ) {
		int j = ej[i][o];

		if (j != p && !path[j] && !dfs2(i, j, d + 1))
			return 0;
	}
	return 1;
}

int main() {
	static int qu[N], qu_[N * 5];
	int n, m, h, i, j, u, v, o, cnt;

	scanf("%d%d", &n, &m);
	if (m != n - 1) {
		printf("NO\n");
		return 0;
	}
	if (n == 1) {
		printf("YES\n");
		printf("1\n");
		printf("1\n");
		return 0;
	}
	if (n == 2) {
		printf("YES\n");
		printf("2\n");
		printf("1 1\n");
		return 0;
	}
	for (i = 0; i < n; i++)
		ej[i] = (int *) malloc(2 * sizeof *ej[i]);
	for (h = 0; h < m; h++) {
		scanf("%d%d", &i, &j), i--, j--;
		append(i, j), append(j, i);
	}
	i_ = -1, d_ = -1;
	dfs1(-1, 0, 0);
	u = i_;
	i_ = -1, d_ = -1;
	dfs1(-1, u, 0);
	v = i_;
	for (h = d_, i = v; h >= 0; h--, i = pp[i])
		path[qu[h] = i] = 1;
	path[u] = path[v] = 0;
	for (h = 1; h < d_; h++)
		if (!dfs2(-1, qu[h], 0)) {
			printf("NO\n");
			return 0;
		}
	cnt = 0;
	for (h = 1; h < d_; h++) {
		i = qu[h];
		for (o = 0; o < eo[i]; o++) {
			j = ej[i][o];
			if (!path[j] && eo[j] >= 2)
				qu_[cnt++] = i, qu_[cnt++] = j;
		}
		qu_[cnt++] = i;
	}
	printf("YES\n");
	printf("%d\n", cnt * 2);
	for (h = 0; h < cnt; h++)
		printf("%d ", qu_[h] + 1);
	for (h = cnt - 1; h >= 0; h--)
		printf("%d ", qu_[h] + 1);
	printf("\n");
	return 0;
}

Compilation message (stderr)

newspapers.c: In function 'append':
newspapers.c:12:23: warning: suggest parentheses around '-' in operand of '&' [-Wparentheses]
   12 |  if (o >= 2 && (o & o - 1) == 0)
      |                     ~~^~~
newspapers.c: In function 'main':
newspapers.c:53:2: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   53 |  scanf("%d%d", &n, &m);
      |  ^~~~~~~~~~~~~~~~~~~~~
newspapers.c:73:3: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   73 |   scanf("%d%d", &i, &j), i--, j--;
      |   ^~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 12 / 12
• Subtask 2: 8 / 8
• Subtask 3: 80 / 80