正解代码

#include<bits/stdc++.h>
using namespace std;
const int N=1e6+10;
int n,a[N],q[N],h,t=-1,k;
int main()
{
	cin>>n>>k;
	for(int i=1;i<=n;++i)
	{
		scanf("%d",&a[i]);
	}
	for(int i=1;i<=n;++i)
	{
		while(h<=t && q[h]<=i-k)h++;
		while(h<=t && a[q[t]]<=a[i])t--;
		q[++t]=i;
		if(i-k>=0)printf("%d",a[q[h]]);
	}
	return 0;
}