14行运行结束后，tail的值不可能小于head。（）

#include 
using namespace std;
const int N = 1000010;
int a[N], q[N];
int main()
{
int n, k;

scanf("%d%d", &n, &k);

for (int i = 0; i < n; i++) scanf("%d", &a[i]);

int head = 0, tail = -1;

for (int i = 0; i < n; i++)

{

    if (head <= tail && i - k + 1 > q[head]) head++;

    while (head <= tail && a[i] < a[q[tail]]) tail--;

    q[++tail] = i;

    if (i + 1 >= k) printf("%d ", a[q[head]]);

}

cout << endl;

return 0;


}