Submission #703230

#	Time	Username	Problem	Language	Result	Execution time	Memory
703230		rainboy	Walking (NOI12_walking)	C11	25 / 25	1 ms	296 KiB

walking

#include <stdio.h>

#define N	500

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

unsigned int X = 12345;

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

int xx[N], pp[N], qq[N];

int compare_x(int i, int j) {
	return xx[i] - xx[j];
}

int compare_pq(int i, int j) {
	return pp[i] * qq[j] - pp[j] * qq[i];
}

int (*compare)(int, int);

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

		while (j < k) {
			int c = compare(ii[j], i_);

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

int ft[N];

void update(int i, int n, int x) {
	while (i < n) {
		ft[i] = max(ft[i], x);
		i |= i + 1;
	}
}

int query(int i) {
	int x = 0;

	while (i >= 0) {
		x = max(x, ft[i]);
		i &= i + 1, i--;
	}
	return x;
}

int main() {
	static int ii[N];
	int n, l, i;

	scanf("%d%d", &l, &n);
	for (i = 0; i < n; i++) {
		int t, v;

		scanf("%d%d", &t, &v);
		xx[i] = t, pp[i] = l + t * v, qq[i] = v;
	}
	for (i = 0; i < n; i++)
		ii[i] = i;
	compare = compare_x, sort(ii, 0, n);
	for (i = 0; i < n; i++)
		xx[ii[i]] = i;
	compare = compare_pq, sort(ii, 0, n);
	for (i = n - 1; i >= 0; i--)
		update(xx[ii[i]], n, query(xx[ii[i]] - 1) + 1);
	printf("%d\n", query(n - 1));
	return 0;
}

Compilation message (stderr)

walking.c: In function 'main':
walking.c:70:2: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   70 |  scanf("%d%d", &l, &n);
      |  ^~~~~~~~~~~~~~~~~~~~~
walking.c:74:3: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
   74 |   scanf("%d%d", &t, &v);
      |   ^~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 3 / 3
• Subtask 2: 3 / 3
• Subtask 3: 5 / 5
• Subtask 4: 7 / 7
• Subtask 5: 7 / 7