Submission #544762

#	Time	Username	Problem	Language	Result	Execution time	Memory
544762		rainboy	The Xana coup (BOI21_xanadu)	C11	100 / 100	130 ms	15700 KiB

xanadu

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

#define N	100000
#define INF	0x3f3f3f3f

int min(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 aa[N], dp[N][2][2];

void dfs(int p, int i) {
	static int xx[2][2], yy[2][2];
	int o, a, b;

	for (o = eo[i]; o--; ) {
		int j = ej[i][o];

		if (j != p)
			dfs(i, j);
	}
	for (a = 0; a < 2; a++)
		xx[a][0] = 0, xx[a][1] = INF;
	for (o = eo[i]; o--; ) {
		int j = ej[i][o];

		if (j != p) {
			for (a = 0; a < 2; a++)
				for (b = 0; b < 2; b++)
					yy[a][b] = min(xx[a][b] + dp[j][a][0], xx[a][b ^ 1] + dp[j][a][1]);
			for (a = 0; a < 2; a++)
				for (b = 0; b < 2; b++)
					xx[a][b] = min(yy[a][b], INF);
		}
	}
	for (a = 0; a < 2; a++)
		for (b = 0; b < 2; b++)
			dp[i][aa[i] ^ a ^ b][a] = xx[a][b] + a;
}

int main() {
	int n, h, i, j, x;

	scanf("%d", &n);
	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);
	}
	for (i = 0; i < n; i++)
		scanf("%d", &aa[i]);
	dfs(-1, 0);
	x = min(dp[0][0][0], dp[0][0][1]);
	if (x == INF)
		printf("impossible\n");
	else
		printf("%d\n", x);
	return 0;
}

Compilation message (stderr)

xanadu.c: In function 'append':
xanadu.c:14:23: warning: suggest parentheses around '-' in operand of '&' [-Wparentheses]
   14 |  if (o >= 2 && (o & o - 1) == 0)
      |                     ~~^~~
xanadu.c: In function 'main':
xanadu.c:53:2: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   53 |  scanf("%d", &n);
      |  ^~~~~~~~~~~~~~~
xanadu.c:57:3: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   57 |   scanf("%d%d", &i, &j), i--, j--;
      |   ^~~~~~~~~~~~~~~~~~~~~
xanadu.c:61:3: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   61 |   scanf("%d", &aa[i]);
      |   ^~~~~~~~~~~~~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 40 / 40
• Subtask 5: 30 / 30