【单调队列】poj2823 Sliding Window

#include<cstdio>
using namespace std;
#define N 1000001
int n,K,a[N],head=1,tail=1,q[N],ans[N];
int main()
{
	scanf("%d%d",&n,&K);
	for(int i=1;i<=n;++i) scanf("%d",&a[i]);
	q[1]=1;
	for(int i=2;i<=K;++i)
	  {
	  	while(a[i]<=a[q[tail]] && tail>=head) --tail;
	  	q[++tail]=i;
	  }
	ans[1]=a[q[head]];
	for(int i=K+1;i<=n;++i)
	  {
	  	if(q[head]<i-K+1) ++head;
	  	while(a[i]<=a[q[tail]] && tail>=head) --tail;
	  	q[++tail]=i;
	  	ans[i-K+1]=a[q[head]];
	  }
	for(int i=1;i<=n-K;++i) printf("%d ",ans[i]);
	printf("%d
",ans[n-K+1]);
	head=tail=1; q[1]=1;
	for(int i=2;i<=K;++i)
	  {
	  	while(a[i]>=a[q[tail]] && tail>=head) --tail;
	  	q[++tail]=i;
	  }
	ans[1]=a[q[head]];
	for(int i=K+1;i<=n;++i)
	  {
	  	if(q[head]<i-K+1) ++head;
	  	while(a[i]>=a[q[tail]] && tail>=head) --tail;
	  	q[++tail]=i;
	  	ans[i-K+1]=a[q[head]];
	  }
	for(int i=1;i<=n-K;++i) printf("%d ",ans[i]);
	printf("%d
",ans[n-K+1]);
	return 0;
}