虽然AC了但还是有地方不理解

这是AC代码：

#include <cstdio>
using namespace std;
const int N = 1000005;
int n, k, a[N], que[N], head = 1, tail = 0;
int main() {
    scanf("%d%d", &n, &k);
    for (int i = 1; i <= n; i ++)
        scanf("%d", &a[i]);
    for (int i = 1; i <= n; i ++) {
        while (head <= tail && i - k + 1 > que[head]) head ++;
        while (head <= tail && a[que[tail]] >= a[i]) tail --;
        que[++ tail] = i;
        if (i >= k) printf("%d ", a[que[head]]);
    }
    printf("\n");
    head = 1, tail = 0;
    for (int i = 1; i <= n; i ++) {
        while (head <= tail && i - k + 1 > que[head]) head ++;
        while (head <= tail && a[que[tail]] <= a[i]) tail --;
        que[++ tail] = i;
        if (i >= k) printf("%d ", a[que[head]]);
    }
    return 0;
}

可是，要是把第12和13行的

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

两条语句调换位置，结果就不一样了，有哪位大佬能解答一下为什么