Codeforces Round #387 (Div. 2), problem: (D) Winter Is Coming Solution in C/C++

Codeforces Round #387 (Div. 2), problem: (D) Winter Is Coming Solution in C/C++

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

int compare(const void *a, const void *b) {
	int *pa = (int *) a;
	int *pb = (int *) b;

	return *pb - *pa;
}

int main() {
	int n, k, i, head, tail, a, b;
	static int aa[200000], bb[200000];

	scanf("%d%d", &n, &k);
	for (i = 0; i < n; i++)
		scanf("%d", &aa[i]);
	a = b = 0;
	head = -1;
	for (i = 0; i < n; i++)
		if (aa[i] < 0) {
			if (head == -1)
				head = a;
			else if (a > 0)
				bb[b++] = a;
			a = 0;
		} else
			a++;
	tail = a;
	if (head == -1)
		printf("0\n");
	else {
		int m, c1, c2, c;

		qsort(bb, b, sizeof(*bb), compare);
		/* case 1: end winter tires */
		m = n - head;
		c1 = 1;
		for (i = 0; i < b && m > k; i++) {
			m -= bb[i];
			c1 += 2;
		}
		if (m > k)
			c1 = INT_MAX;
		/*case 2: end summer tires */
		m = n - head - tail;
		c2 = 2;
		for (i = 0; i < b && m > k; i++) {
			m -= bb[i];
			c2 += 2;
		}
		if (m > k)
			c2 = INT_MAX;
		c = c1 < c2 ? c1 : c2;
		printf("%d\n", c == INT_MAX ? -1 : c);
	}
	return 0;
}